JPWO2012063285A1 - Organic EL display panel and driving method thereof - Google Patents

Abstract

An organic EL display panel (1), a p-type driving transistor (22) having a gate connected to a capacitor (24) and a drain connected to an organic EL element (25), and a gate connected to the capacitor (24) An n-type drive transistor (23) whose source is connected to the organic EL element (25), a first power supply line (14) for applying a first voltage to the p-type drive transistor (22), and a first power supply line (14) to the n-type drive transistor. A second power supply line (13) for applying a second voltage higher than one voltage, and the p-type drive transistor (22) has a first current value corresponding to a predetermined current value in a current-voltage characteristic of the organic EL element (25). The n-type driving transistor (23) has a characteristic that the gate voltage value is the minimum voltage of the data voltage, and the n-type driving transistor (23) has a second gate voltage value corresponding to the predetermined current value corresponding to the minimum current value of the organic EL element (25). A third is a higher voltage value than the gate voltage characteristics.

Description

  The present invention relates to an organic EL display panel and a driving method thereof, and more particularly to an organic EL display panel using an active matrix driving circuit and a driving method thereof.

  As a display panel using a current-driven light emitting element, a display panel using an organic electroluminescence (EL) element is known. The organic EL display panel using the organic EL element that emits light does not require the backlight necessary for the liquid crystal display panel, and is optimal for thinning the device. Moreover, since there is no restriction | limiting also in a viewing angle, utilization as a next-generation display panel is anticipated. Further, the organic EL element used in the organic EL display panel is different from the liquid crystal cell being controlled by the voltage applied thereto, in that the luminance of each light emitting element is controlled by the current value flowing therethrough.

  In an organic EL display panel, organic EL elements constituting pixels are usually arranged in a matrix. An organic EL element is provided at the intersection of a plurality of row electrodes (scanning lines) and a plurality of column electrodes (data lines), and a voltage corresponding to a data signal is applied between the selected row electrodes and the plurality of column electrodes. A device for driving an organic EL element is called a passive matrix type organic EL display.

  On the other hand, a switching thin film transistor (TFT) is provided at the intersection of a plurality of scanning lines and a plurality of data lines, the gate of the driving TFT is connected to the switching TFT, and the switching TFT is turned on through the selected scanning line. Then, a data signal is input from the signal line to the driving TFT. A device in which the organic EL element is driven by the driving TFT is called an active matrix type organic EL display panel.

  The active matrix organic EL display panel differs from the passive matrix organic EL display panel in which the organic EL element connected thereto emits light only during the period when each row electrode (scanning line) is selected. Since the organic EL element can emit light until the selection), the luminance of the display is not reduced even if the number of scanning lines is increased. In this respect, the active matrix driving method is advantageous in realizing a large screen and a high-definition display panel.

  On the other hand, an organic EL display panel using a current-driven organic EL element emits light when a current flows through the organic EL element of each pixel, so that it is compared with a liquid crystal element that is a voltage-driven element. Therefore, the power consumption of the display panel tends to increase. In particular, the power consumption of the display panel increases with an increase in screen size and resolution.

  Patent Document 1 discloses a circuit configuration for reducing power consumption of a pixel portion in an active matrix organic EL display device.

  FIG. 17 is a circuit diagram illustrating an example of a specific circuit configuration of a pixel circuit included in the organic EL display device described in Patent Document 1. As shown in the figure, the light emitting pixel 100A includes a selection transistor 121b for writing the voltage of the data line 112 to the storage capacitor element 124b when the light emitting pixel 100A is selected by the scanning signal from the scanning line 111. , The storage capacitor element 124b, the p-type drive transistor 122 that causes the drive current corresponding to the storage voltage of the storage capacitor element 124b to flow from the high luminance power line 113 or the low luminance power line 114 to the reference power line 115, and the driving And an organic EL element 125 that emits light when a current flows. The above pixel configuration is a configuration provided in a normal pixel circuit.

  Further, the light emitting pixel 100A includes a switching transistor 123 for turning on / off the high-brightness power supply voltage from the high-brightness power supply line 113 and a diode 126 for turning on / off the low-brightness power supply voltage from the low-brightness power supply line 114. A storage capacitor element 124a having one end connected to the high-brightness power supply line 113 and the other end connected to the gate of the switching transistor 123; and a gate connected to the scanning line 111; A selection transistor 121a that inputs a control signal VELS to the gate of the switching transistor 123 when 100A is selected. The source of the switching transistor 123 and the cathode of the diode 126 are commonly connected, and the source of the p-type drive transistor 122 is connected to the common connection point.

  The switching transistor 123, the selection transistor 121 a, the storage capacitor element 124 a, and the diode 126 described above use either a high-brightness power supply voltage or a low-brightness power supply voltage as a pixel power supply voltage supplied to the p-type drive transistor 122. A power supply voltage switching means for switching whether or not to perform is configured.

  In the above circuit configuration, when the power supply voltage for high luminance is selected, the scanning signal and the control signal VELS are simultaneously at the high level during the writing period. In this case, the switching transistor 123 is turned on, and the power supply voltage for high brightness is supplied to the source of the p-type drive transistor 122. At this time, since the anode potential becomes the low-brightness power supply voltage and the cathode potential becomes the high-brightness power supply voltage, the diode 126 is in a reverse bias state and is automatically turned off. The power supply voltage is cut off.

  On the other hand, when the power supply voltage for low luminance is selected, only the scanning signal becomes high level during the writing period, and the control signal VELS maintains low level. In this case, the switching transistor 123 is turned off, and the power supply voltage from the high luminance power supply line 113 is cut off. At this time, the diode 126 is forward biased and turned on, and the low-brightness power supply voltage is supplied to the source of the p-type drive transistor 122.

  As described above, in the circuit configuration shown in FIG. 17, the diode 126 is turned on / off by turning on / off the switching transistor 123 by the control signal VELS.

  Here, the voltage level of the control signal VELS is determined as follows by the scanning line driving circuit to which the scanning line 111 is connected. For example, when all the display gradations are expressed by 256 gradations, when the gradation signal value of the light emitting pixel 100A belongs to the high gradation side when the 128 gradation values are used as the reference value, the high luminance is obtained. The control signal VELS is set to a high level so as to select a power supply voltage for low power, and when belonging to the low gradation side, the control signal VELS is set to a low level so as to select a power supply voltage for low luminance.

  With the above configuration, the organic EL display device described in Patent Document 1 is provided with a high-brightness power supply voltage and a low-brightness power supply voltage, and individually controls the pixel voltage for each pixel circuit by the control signal VELS. As a result, a circuit configuration is provided in which a reduction in image quality is surely prevented and power consumption is also reduced.

JP 2008-89726 A

  However, in the organic EL display device described in Patent Document 1, in order to select a low power supply voltage as a pixel power supply used at the time of low gradation display, in addition to a circuit configuration essential for a normal pixel circuit, power supply voltage switching means As described above, a selection transistor 121a, a storage capacitor element 124a, and a diode 126 are required for each light emitting pixel. Further, a control line for applying the control signal VELS to the gate of the switching transistor 123 must be provided separately from the scanning line driving circuit. These circuit components and wiring increase the circuit scale of the pixel circuit, which is inconvenient for high definition display panels.

  Further, the scanning line driving circuit has to switch the voltage level of the control signal VELS for each light emitting pixel, which increases the load of switching the voltage of the output signal from the driving circuit.

  In view of the above problems, the present invention realizes low power consumption with a simple pixel circuit configuration without significantly increasing the number of elements of the pixel circuit even when the light-emitting pixel is miniaturized and high-definition progresses. An object of the present invention is to provide an organic EL display panel and a driving method thereof.

  In order to achieve the above object, an organic EL display panel according to an aspect of the present invention includes an organic EL element, a capacitor having a first electrode and a second electrode, and holding a voltage corresponding to a data voltage; A gate electrode is connected to the first electrode of the capacitor, a drain electrode is connected to the anode electrode of the organic EL element, and a first drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. Thus, the p-type first driving transistor for causing the organic EL element to emit light, the gate electrode is connected to the first electrode of the capacitor, the source electrode is connected to the anode electrode of the organic EL element, and held by the capacitor In addition, an n-type second drive transistor that emits light from the organic EL element by supplying a second drain current corresponding to the voltage to the organic EL element. A data line for supplying the data voltage, a switching transistor for holding the voltage in the capacitor by switching conduction and non-conduction between the data line and the capacitor, and the first drive transistor A first power supply line for applying a first power supply voltage to the source electrode of the second drive transistor, and a second power supply line for applying a second power supply voltage higher than the first power supply voltage to the drain electrode of the second drive transistor, In the one drive transistor, a first gate voltage value corresponding to a predetermined current value in the current-voltage characteristic of the organic EL element is a minimum voltage in the data voltage, and the first drain current is smaller than the predetermined current value. It is a transistor having a current-voltage characteristic such that the gate voltage for flowing the first drain current increases. In the second drive transistor, the second gate voltage value corresponding to the predetermined current value is a voltage value larger than a third gate voltage value corresponding to the minimum current value passed through the organic EL element, The transistor has a current-voltage characteristic such that a gate voltage for allowing the second drain current to flow increases as the second drain current becomes larger than the predetermined current value.

  According to the organic EL display panel and the driving method thereof of the present invention, two drive transistors are required for each light-emitting pixel in order to reduce power consumption, but a switching circuit between a high voltage power line and a low voltage power line. Without increasing the number of drive transistors, and by increasing the number of drive transistors by one without arranging two data lines and two select transistors corresponding to the two drive transistors, The high voltage power line and the low voltage power line are automatically selected. As a result, an energy-saving pixel circuit can be realized with a simple configuration without significantly increasing the circuit elements of the light emitting pixels.

FIG. 1 is a functional block diagram of an organic EL display panel according to an embodiment of the present invention. FIG. 2 is a circuit diagram of the light emitting pixel according to the embodiment of the present invention. FIG. 3 is a graph schematically showing current-voltage characteristics of the organic EL element. FIG. 4 is a graph showing current-voltage characteristics of two drive transistors according to the embodiment of the present invention. FIG. 5A is a graph showing current-voltage characteristics of the p-type drive transistor according to the exemplary embodiment of the present invention. FIG. 5B is a graph showing current-voltage characteristics of the n-type drive transistor according to the exemplary embodiment of the present invention. FIG. 6 is a graph showing the conversion characteristics of the conversion circuit according to the embodiment of the present invention. FIG. 7A is a diagram showing the flow of various signals in the organic EL display panel according to the embodiment of the present invention. FIG. 7B is a drive timing chart of the organic EL display panel according to the embodiment of the present invention. FIG. 8 is a diagram showing the relationship of the operation flow of each circuit included in the organic EL display panel according to the embodiment of the present invention. FIG. 9 is an operation flowchart of the light-emitting pixel circuit according to the embodiment of the present invention. FIG. 10 is an example of a driving timing chart for explaining in detail the driving operation of the organic EL display panel according to the embodiment of the present invention. FIG. 11 is a graph showing an example of the conversion characteristics of the conversion circuit according to the embodiment of the present invention. FIG. 12 is a diagram illustrating a circuit state of the light emitting pixels in the adjacent row according to the embodiment of the present invention. FIG. 13 is a graph showing an example of current-voltage characteristics of two drive transistors according to the embodiment of the present invention. FIG. 14 is a circuit diagram of a luminescent pixel showing a modification according to the embodiment of the present invention. FIG. 15 is a graph showing current-voltage characteristics of two drive transistors included in a light emitting pixel according to a modification according to the embodiment of the present invention. FIG. 16 is an external view of a thin flat TV incorporating the organic EL display panel of the present invention. FIG. 17 is a circuit diagram illustrating an example of a specific circuit configuration of a pixel circuit included in the organic EL display device described in Patent Document 1.

  In order to achieve the above object, an organic EL display panel according to an aspect of the present invention includes an organic EL element, a capacitor having a first electrode and a second electrode, and holding a voltage corresponding to a data voltage; A gate electrode is connected to the first electrode of the capacitor, a drain electrode is connected to the anode electrode of the organic EL element, and a first drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. Thus, the p-type first driving transistor for causing the organic EL element to emit light, the gate electrode is connected to the first electrode of the capacitor, the source electrode is connected to the anode electrode of the organic EL element, and held by the capacitor In addition, an n-type second drive transistor that emits light from the organic EL element by supplying a second drain current corresponding to the voltage to the organic EL element. A data line for supplying the data voltage, a switching transistor for holding the voltage in the capacitor by switching conduction and non-conduction between the data line and the capacitor, and the first drive transistor A first power supply line for applying a first power supply voltage to the source electrode of the second drive transistor, and a second power supply line for applying a second power supply voltage higher than the first power supply voltage to the drain electrode of the second drive transistor, In the one drive transistor, a first gate voltage value corresponding to a predetermined current value in the current-voltage characteristic of the organic EL element is a minimum voltage in the data voltage, and the first drain current is smaller than the predetermined current value. It is a transistor having a current-voltage characteristic such that the gate voltage for flowing the first drain current increases. In the second drive transistor, the second gate voltage value corresponding to the predetermined current value is a voltage value larger than a third gate voltage value corresponding to the minimum current value passed through the organic EL element, The transistor has a current-voltage characteristic in which a gate voltage for flowing the second drain current increases as the second drain current becomes larger than the predetermined current value.

  According to this aspect, two power supply lines having different power supply voltages are provided, and the first power supply line and the second power supply line are selectively used according to the data voltage. Therefore, the high power supply voltage prepared as the maximum value for any data voltage is not supplied, but only when the data voltage requires a high power supply voltage for light emission with accurate brightness. The power supply voltage will be used. As a result, power consumption can be greatly reduced as compared with the case where a high power supply voltage is supplied to any data voltage.

  In addition, according to this aspect, two power supply lines are provided, and when the first power supply line and the second power supply line are selected according to the data voltage, the p-type first transistor is used as a drive transistor for driving the organic EL element. There are provided drive transistors having opposite polarities, that is, a drive transistor and an n-type second drive transistor. The source electrode of the p-type first drive transistor is connected to the first power supply line, and the drain electrode of the n-type second drive transistor is connected to the second power supply line.

  In addition, the first drive transistor has a minimum gate voltage when a predetermined current value in the current-voltage characteristic of the organic EL element flows as the first drain current, and the first drain current is greater than the predetermined current value. The transistor has current-voltage characteristics such that the gate voltage value for flowing the first drain current increases as the value decreases. On the other hand, in the second drive transistor, the gate voltage value when the predetermined current value flows as the second drain current is a voltage value larger than the gate voltage value corresponding to the minimum current value flowing through the organic EL element. The transistor has current-voltage characteristics such that the gate voltage value for flowing the second drain current increases as the drain current becomes larger than the predetermined current value. Note that the minimum current value flowing through the organic EL element is a current value when the forward current starts to flow exceeding the threshold voltage in the organic EL element having diode characteristics, and is a current at which the organic EL element starts to emit light. is there.

  As a result, although the number of drive transistors increases by one, a data line and a switching transistor are provided for each of the two drive transistors without adding a switching circuit between the first power supply line and the second power supply line. Without increasing the number of driving transistors, the first power supply line and the second power supply line can be selectively used according to the data voltage. As a result, an energy-saving pixel circuit with low power consumption can be realized with a simple configuration without significantly increasing the circuit elements of the light-emitting pixels.

  In the organic EL display panel according to an aspect of the present invention, the fourth gate voltage value corresponding to the minimum current value flowing through the organic EL element in the current-voltage characteristics of the first drive transistor is the third voltage. The gate voltage is preferably smaller than

  According to this aspect, the range of the gate voltage for flowing the first drain current by the p-type first drive transistor and the range of the gate voltage for flowing the second drain current by the n-type second drive transistor overlap. Rather, it is completely separated. As a result, the organic EL element can be caused to emit light by the drain current supplied from only one of the driving transistors at all data voltages without adding a switching circuit between the high voltage power line and the low voltage power line. Is possible.

  The organic EL display panel according to an aspect of the present invention further includes a conversion circuit that converts video data into a conversion data signal, and a DA conversion that converts the conversion data signal input from the conversion circuit into the data voltage. It is preferable that the data line driving circuit includes a circuit and supplies the data voltage to the data line.

  In this aspect, the data line driving circuit does not input the data voltage corresponding to the video data as it is, but converts the data voltage obtained by analog conversion of the converted data signal that has undergone predetermined conversion via the conversion circuit. Supply to the data line.

  Further, in the organic EL display panel according to one aspect of the present invention, the conversion circuit has the first gate voltage value in the current-voltage characteristic of the first drive transistor, wherein the data voltage corresponding to the converted data signal is To the fourth gate voltage value, the converted data signal is converted so that the converted data voltage becomes smaller as the display gradation of the video data corresponding to the range increases, and the converted data signal When the data voltage corresponding to the range is equal to or higher than the second gate voltage value in the current-voltage characteristic of the second driving transistor, the converted video data corresponding to the range increases as the display gradation of the video data increases. It is preferable to convert the converted data signal so that the data voltage is increased.

  According to this aspect, even when the organic EL element is driven using two drive transistors whose polarities are inverted from each other, the data voltage is in a range corresponding to the converted data signal obtained by converting the video data. Accordingly, a data voltage corresponding to the entire area from the minimum value to the maximum value of the video data can be generated.

  As a result, the data voltage corresponding to the converted data signal corresponds to the minimum current value that flows from the first gate voltage value corresponding to the predetermined current value to the organic EL element in the current-voltage characteristics of the first drive transistor. Corresponding to video data in the range up to the fourth gate voltage value and in the current-voltage characteristic of the second drive transistor in the range equal to or higher than the second gate voltage value corresponding to the predetermined current value. Although the control for increasing / decreasing the conversion data signal to be performed is different, the entire region from the minimum value to the maximum value of the video data is used even when the organic EL element is driven by using two drive transistors having opposite polarities. The data voltage corresponding to can be generated.

  The organic EL display panel according to an aspect of the present invention further includes a scanning line driving circuit that outputs a scanning signal for controlling conduction and non-conduction of the switching transistor to the switching transistor through the scanning line. Is preferred.

  According to this aspect, the supply timing of the data voltage to the light emitting pixel is determined by the scanning signal output from the scanning line driving circuit to the switching transistor via the scanning line.

  In the organic EL display panel according to one embodiment of the present invention, pixel circuits including the organic EL element, the capacitor, the first driving transistor, and the second driving transistor may be arranged in a matrix. .

  As a result, the number of drive transistors is increased by one in each pixel circuit, and the first power supply line and the second power supply line can be selectively used according to the data voltage. As a result, the display panel as a whole having light emitting pixels arranged in a matrix can be realized with a simple configuration without significantly increasing circuit elements.

  The organic EL display panel according to an aspect of the present invention further includes a control circuit for controlling the data line driving circuit and the scanning line driving circuit, and the control circuit is configured to control the matrix by the scanning line driving circuit. The switching circuit included in each pixel circuit in a certain line is ON-controlled, and the data voltage is supplied to each pixel circuit in the certain line via the data line by the data line driving circuit. You may perform control which synchronizes with a timing.

  According to this aspect, the supply timing of the data voltage from the data line driving circuit and the supply timing of the scanning signal from the scanning line driving circuit are synchronized in row order. Thereby, row sequential scanning of panel light emission is realized.

  Further, in the organic EL display panel according to one embodiment of the present invention, the data line driving circuit is configured such that each pixel circuit in one matrix-like line from the scanning line driving circuit is input by a synchronization signal from the control circuit. The data voltage may be supplied to the pixel circuits in the certain line via the data line in synchronization with the timing of outputting the scanning signal.

  According to this aspect, even when the conversion circuit is arranged in the preceding stage of the data line driving circuit and the conversion tendency of the data voltage is changed according to the video signal, the converted data voltage is synchronized with the scanning signal. It is possible to output from the line drive circuit.

  In addition, the present invention can be realized not only as an organic EL display panel including such characteristic means but also as an organic EL display device including the organic EL display panel.

  The present invention can be realized not only as an organic display panel having such characteristic means, but also as a method for driving an organic EL display panel using characteristic means included in the organic EL display panel as a step. Can be realized.

  In addition, an organic EL display panel according to one embodiment of the present invention includes an organic EL element, a first electrode and a second electrode, a capacitor holding a voltage corresponding to a data voltage, and a gate electrode of the capacitor. The organic EL element is connected to the first electrode, the drain electrode is connected to the cathode electrode of the organic EL element, and a first drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. An n-type first driving transistor that emits light, a gate electrode connected to the first electrode of the capacitor, a source electrode connected to a cathode electrode of the organic EL element, and according to the voltage held in the capacitor A p-type second drive transistor that emits light from the organic EL element by supplying a second drain current to the organic EL element; A data line for supplying the data, a switching transistor for holding the data voltage in the first electrode of the capacitor by switching between conduction and non-conduction between the data line and the capacitor, and A first power supply line for setting a first power supply voltage on the source electrode; and a second power supply line for setting a second power supply voltage lower than the first power supply voltage on the drain electrode of the second drive transistor, In the driving transistor, the first gate voltage value corresponding to the predetermined current value in the current-voltage characteristic of the organic EL element is the maximum voltage in the data voltage, and the first drain current is smaller than the predetermined current value. The transistor has a current-voltage characteristic such that the gate voltage for flowing the first drain current is small. In the second driving transistor, a second gate voltage value corresponding to the predetermined current value is smaller than a third gate voltage value corresponding to a minimum current value passed through the organic EL element, and The transistor may have a current-voltage characteristic such that the gate voltage for flowing the second drain current decreases as the 2-drain current becomes larger than the predetermined current value.

  According to this aspect, even in the circuit configuration in which the drive transistor is connected to the cathode side of the organic EL element, the same effect as the organic EL display panel having the circuit configuration in which the drive transistor is connected to the anode side of the organic EL element is obtained. Played.

(Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a functional block diagram of an organic EL display panel according to an embodiment of the present invention. The organic EL display panel 1 in FIG. 1 includes a control circuit 2, a scanning line driving circuit 3, a data line driving circuit 4, a power supply circuit 5, a display unit 6, and a conversion circuit 7.

  The display unit 6 includes a plurality of light emitting pixels 6A arranged in a matrix. The data voltage Vdata is supplied to the light emitting pixel 6A via a data line arranged for each light emitting pixel column. The scanning signal SCAN is supplied to the light emitting pixel 6A via a scanning line arranged for each light emitting pixel row.

  The scanning line driving circuit 3 drives the circuit elements included in the light emitting pixels 6A by sequentially outputting the scanning signals SCAN to the scanning lines arranged for each row. The scanning signal SCAN is a signal for switching between conduction and non-conduction of the switching transistor of the light emitting pixel 6A. Specifically, the scanning line driving circuit 3 supplies the scanning signal SCAN to the light emitting pixels 6 </ b> A in response to the input of the start pulse signal from the control circuit 2.

  The data line driving circuit 4 drives a circuit element of the light emitting pixel by outputting a data voltage based on the video signal to the data line arranged for each column. Specifically, the data line driving circuit 4 synchronizes with the timing at which the scanning signal is output from the scanning line driving circuit 3 to the light emitting pixels 6A in a row-sequential manner by the input of the synchronizing signal from the control circuit 2, and the data voltage is set. The light is supplied to the light emitting pixel 6A. The data line driving circuit 4 includes a DA (digital / analog) conversion circuit that converts a converted data signal that is a digital signal input from the conversion circuit 7 into a data voltage that is an analog signal.

  The control circuit 2 controls the output timing of the scanning signal SCAN output from the scanning line driving circuit 3. The control circuit 2 controls the timing for outputting the data voltage output from the data line driving circuit 4. Specifically, the timing at which the switching transistor of the light emitting pixel 6A is turned on is controlled by outputting a start pulse signal to the scanning line driving circuit 3 based on a video signal input from the outside. In addition, by outputting a synchronization signal to the data line driving circuit 4, control is performed to synchronize the timing for supplying the data voltage output from the data line driving circuit 4 and the output timing of the scanning signal SCAN.

  The power supply circuit 5 supplies a constant power supply voltage to all the light emitting pixels 6A via each power supply line.

  The conversion circuit 7 converts video data, which is luminance information of a video signal input from the outside, into a converted data signal. A specific conversion method will be described later with reference to FIG.

FIG. 2 is a circuit diagram of the light emitting pixel according to the embodiment of the present invention. The light emitting pixel 6 </ b> A shown in the figure includes a selection transistor 21, a p-type drive transistor 22, an n-type drive transistor 23, a capacitor 24, and an organic EL element 25. A data line 12 is arranged for each light emitting pixel column, and a scanning line 11 is arranged for each light emitting pixel row. Further, the first power supply line 14, the second power supply line 13, the reference power supply line 15, and the reference power supply line 16 are arranged for all the light emitting pixels 6A. The first power supply line 14, the second power supply line 13, the reference power supply line 15, and the reference power supply line 16 are also connected to other light emitting pixels, and are connected to the power supply circuit 5. Further, the high voltage V _DD1 set on the second power supply line 13 is set higher than the low voltage V _DD2 set on the first power supply line 14, and both the first power supply line 14 and the second power supply line 13 are set. The potential is set higher than that of the reference power line 15.

  The data line 12 is connected to the data line driving circuit 4 and connected to each light emitting pixel belonging to the pixel column including the light emitting pixel 6A. As a result, the data voltage Vdata that determines the light emission intensity is supplied to the light emitting pixel 6A via the data line 12.

  The scanning line 11 is connected to the scanning line driving circuit 3 and is connected to each light emitting pixel belonging to the pixel row including the light emitting pixel 6A. Accordingly, the scanning signal SCAN indicating the timing for writing the data voltage Vdata is supplied to the light emitting pixel 6A via the scanning line 11.

  The selection transistor 21 is a switching transistor in which the gate electrode is connected to the scanning line 11 and one of the source electrode and the drain electrode is connected to the gate electrodes of the p-type driving transistor 22 and the n-type driving transistor 23. The selection transistor 21 switches the conduction and non-conduction between the data line 12 and the capacitor 24 according to the scanning signal SCAN from the scanning line 11 to cause the capacitor 24 to hold a voltage corresponding to the data voltage. The selection transistor 21 is composed of, for example, an n-type thin film transistor (n-type TFT).

  The p-type drive transistor 22 has a gate electrode connected to the first electrode of the capacitor 24, a drain electrode connected to the anode electrode of the organic EL element 25, and a source electrode connected to the first power supply line 14. Due to the above connection relationship, the p-type drive transistor 22 supplies the first drain current to the organic EL element 25 in accordance with the voltage held in the capacitor 24 to cause the organic EL element 25 to emit light. The p-type drive transistor 22 is composed of a p-type thin film transistor (p-type TFT). Here, the first drain current is a current that flows from the first power supply line 14 to the reference power supply line 15 via the p-type drive transistor 22.

  The n-type drive transistor 23 has a gate electrode connected to the first electrode of the capacitor 24, a source electrode connected to the anode electrode of the organic EL element 25, and a drain electrode connected to the second power supply line 13. With the above connection relationship, the n-type drive transistor 23 supplies the second drain current to the organic EL element 25 according to the voltage held in the capacitor 24 to cause the organic EL element 25 to emit light. The n-type drive transistor 23 is composed of an n-type thin film transistor (n-type TFT). Here, the second drain current is a current that flows from the second power supply line 13 to the reference power supply line 15 via the n-type drive transistor 23.

  The organic EL element 25 is a light emitting element having an anode electrode connected to the drain electrode of the p-type drive transistor 22 and the source electrode of the n-type drive transistor 23, and a cathode electrode connected to the reference power supply line 15. Due to the above connection relationship, the organic EL element 25 emits light when the first drain current of the p-type drive transistor 22 or the second drain current of the n-type drive transistor 23 flows.

  The capacitor 24 has a first electrode connected to the gate electrodes of the p-type drive transistor 22 and the n-type drive transistor 23, and a second electrode connected to the reference power supply line 16, and holds a voltage corresponding to the data voltage. For example, after the selection transistor 21 is turned off, the gate-source voltage of the p-type drive transistor 22 and the n-type drive transistor 23 is stably maintained, and the first and second drain currents are stabilized. Have.

Here, the first drain current supplied from the p-type drive transistor 22 and the second drain current supplied from the n-type drive transistor 23 are selectively set with a predetermined current value in the current-voltage characteristics of the organic EL element 25 as a threshold value. Are set to flow through the organic EL element 25. That is, in each display gradation, one of the first drain current and the second drain current flows through the organic EL element 25, so that one of the drain currents becomes the light emission current of the organic EL element 25. In the light emitting pixel 6A, for example, in the low light emission current region, the p-type drive transistor 22 is turned on and the first drain current flows as the light emission current. In the high light emission current region, the n-type drive transistor 23 is turned on and the second drain current flows as the light emission current. For this reason, in the low light emission current region, the first drain current flows from the first power supply line 14 where the low voltage V _DD2 is set to the organic EL element 25. Therefore, in the display operation in the low light emission current region, the power consumption can be reduced as compared with the case where the drain current flows from the second power supply line 13.

  That is, in the light emitting pixel 6A according to the embodiment of the present invention, the number of driving transistors is increased by one as compared with a normal light emitting pixel circuit, but switching between the first power supply line 14 and the second power supply line 13 is performed. By increasing the number of driving transistors by one without increasing the number of circuits and without providing a data line and a selection transistor for every two driving transistors, the first power supply line can be selected according to the data voltage. 14 and the second power supply line 13 can be used properly. As a result, an energy-saving pixel circuit with low power consumption can be realized with a simple configuration without significantly increasing the circuit elements of the light-emitting pixels.

  Hereinafter, in the organic EL display panel 1 of the present invention, the first drain current and the second drain current are changed according to the display gradation without adding a switching circuit between the first power line 14 and the second power line 13. A configuration for realizing selection will be described.

  FIG. 3 is a graph schematically showing current-voltage characteristics of the organic EL element. In the figure, the horizontal axis represents the voltage applied between the anode and cathode of the organic EL element, and the vertical axis represents the forward current. As shown in the figure, the current-voltage characteristics of the organic EL element 25 are diode characteristics. When a voltage equal to or higher than a predetermined threshold voltage is applied between the anode and the cathode, a forward current starts to flow, and the current monotonously increases as the voltage increases.

  Here, in the organic EL display panel 1 according to the embodiment of the present invention, a predetermined current value Ia is defined in the current-voltage characteristics of the organic EL element 25. With the current Ia emitted from the organic EL element 25 as a boundary current, light is emitted to the organic EL element 25 via the second power supply line 13 and the n-type drive transistor 23 that supply a high power supply voltage in a current region larger than Ia. In the current region below Ia, a light emission current is supplied to the organic EL element 25 via the first power supply line 14 and the p-type drive transistor 22 that supply a low power supply voltage.

  Next, current-voltage characteristics of the p-type drive transistor 22 and the n-type drive transistor 23 for flowing either the first drain current or the second drain current to the organic EL element 25 using Ia as a threshold will be described.

FIG. 4 is a graph showing current-voltage characteristics of two drive transistors according to the embodiment of the present invention. In the figure, the horizontal axis represents the data voltage Vdata, that is, the voltage applied to the gate electrode of the driving transistor, and the vertical axis represents the drain current Id of the driving transistor. The first gate voltage value is V _L2 , the second gate voltage value is V _H1 , the third gate voltage value is V _H0 , and the fourth gate voltage value is V _L1 .

The p-type driving transistor 22 is data in which the first gate voltage value V _L2 when the current Ia in the current-voltage characteristic of the organic EL element 25 shown in FIG. The current-voltage characteristic is such that the gate voltage for allowing the first drain current to flow increases as the first drain current becomes smaller than the current Ia. In other words, it has a current-voltage characteristic in which the first drain current decreases as the gate voltage increases.

On the other hand, the n-type drive transistor 23 has a third gate voltage value V _H1 corresponding to the minimum current value Imin that flows through the organic EL element 25 when the current Ia flows as the second drain current. _The voltage value is higher than _H0 , and the current-voltage characteristic is such that the gate voltage for flowing the second drain current increases as the second drain current becomes larger than the current Ia. In other words, it has a current-voltage characteristic in which the second drain current increases as the gate voltage increases. In addition, the n-type drive transistor 23 causes the current Ib to flow as the second drain current when the gate voltage value is _VH2 . Here, the current value Imin is a current value on the horizontal axis in the current-voltage characteristic shown in FIG. 4, and a current smaller than the current value can be ignored as a light emission current.

Note that the fourth gate voltage value V _L1 corresponding to the minimum current value Imin that flows through the organic EL element in the current-voltage characteristics of the p-type drive transistor 22 is set smaller than the third gate voltage value V _H0 . It is preferable.

  As a result, the range of the gate voltage for flowing the first drain current by the p-type drive transistor 22 and the range of the gate voltage for flowing the second drain current by the n-type drive transistor 23 do not overlap and are completely separated. The As a result, the organic EL element 25 is caused to emit light by the drain current supplied from only one of the drive transistors at all data voltages without adding a switching circuit between the high voltage power line and the low voltage power line. It becomes possible.

The potential difference between the second gate voltage value V _H1 and the third gate voltage value V _H0 of the n-type drive transistor 23 is the fourth gate voltage value V _L1 of the p-type drive transistor 22 and the first gate voltage. It is preferable that the potential difference with the value V _L2 is smaller. Furthermore, it is preferable that the potential difference between the second gate voltage value V _H1 and the third gate voltage value V _H0 of the n-type drive transistor 23 is as small as possible.

The drain current supplied to the organic EL element 25 starts to flow when the gate voltage corresponding to the fourth gate voltage value _VL1 is applied to the gate electrode of the p-type drive transistor 22, and the first drain current starts to flow. as the current increases, the gate voltage is reduced to the first gate voltage V _L2. When the first drain current value reaches a predetermined current value Ia, a voltage corresponding to the second gate voltage value V _H1 is applied to the gate electrode of the n-type drive transistor 23, so that the second drain current flows. start. That is, the voltage range in which neither the p-type drive transistor 22 nor the n-type drive transistor 23 passes current is a voltage range corresponding to the range between the fourth gate voltage value V _L1 and the second gate voltage value V _H1. It is. By reducing this range, that is, by making the slope of the current-voltage characteristic of the n-type drive transistor 23 in that range steep, the second gate voltage value V _H1 is as low as possible (V _H1 ′ → V _H1 ) can be set, the voltage for flowing the second drain current flowing through the second drive transistor can be reduced, and the power consumption can be reduced.

The potential difference between the fourth gate voltage value V _L1 and the first gate voltage value V _L2 of the p-type drive transistor 22 is the second gate voltage value V _H1 of the n-type drive transistor 23 and the third gate voltage. It is preferable that the potential difference is larger than the value V _H0 . The potential difference between the fourth gate voltage value V _L1 and the first gate voltage value V _L2 of the p-type drive transistor 22 is used as the second gate voltage value V _H1 and the third gate voltage value V _H0 of the n-type drive transistor 23. The number of displayable gradations in the low gradation region can be increased. The reason is described below.

The data voltage applied to each gate electrode of the p-type drive transistor 22 and the n-type drive transistor 23 is applied with a predetermined minimum resolution. For example, if 0.01V is the minimum resolution, a data voltage can be input in units of 0.01V. Therefore, for example, the potential difference between the second gate voltage value V _H1 and the third gate voltage value V _H0 of the n-type drive transistor 23 is set to 0.5 V, and the fourth gate voltage value of the p-type drive transistor 22 is set. Assume that the potential difference between V _L1 and the first gate voltage value V _L2 is set to 1V. In this case, 50 gradations can be assigned in the drain current range of Ia or less between the potential difference between the second gate voltage value V _H1 and the third gate voltage value V _H0 of the n-type drive transistor 23. On the other hand, between the potential difference between the fourth gate voltage value V _L1 and the first gate voltage value V _L2 of the p-type drive transistor 22, 100 gradations can be assigned in the same drain current range. In the organic EL display panel 1 according to the present embodiment, the first drain current flowing through the p-type drive transistor 22 flows to the organic EL element 25 at a predetermined current value Ia or less. Therefore, the current control in the low gradation region is performed not by the number of gradations of the n-type driving transistor 23 but by the number of gradations of the p-type driving transistor 22. As a result, the number of gradations in the drain current range below the predetermined current value Ia can be set so that the outputable gradation in the low gradation region of the organic EL element 25 also increases. In particular, since the human eye has high luminance sensitivity in the low gradation range, the displayable gradation in the low gradation range increases, so that the quality of the representable color of the display device can be improved.

  Next, the voltage in the current-voltage characteristics of the p-type drive transistor 22 and the n-type drive transistor 23 described above is expressed by a gate-source voltage.

FIG. 5A is a graph showing current-voltage characteristics of the p-type drive transistor according to the exemplary embodiment of the present invention. With respect to the gate voltage value applied to the gate electrode of the p-type drive transistor 22, the gate-source voltage Vgs is a value obtained by subtracting V _DD2 that is the voltage of the source electrode from the gate voltage value. Therefore, it is possible to set the range of the data voltage for flowing the first drain current of the p-type drive transistor 22 and the range of Vgs to the same (V _L1 −V _L2 ).

As described above, from the characteristics of the drive transistor shown in FIGS. 4, 5 </ b> A, and 5 </ b> B, V _{L1 to} V _L2 are set as the data voltage range for flowing the first drain current of the p-type drive transistor 22 to the organic EL element 25. By setting V _{H1 to} V _H2 as a data voltage range for setting the second drain current of the n-type drive transistor 23 to flow through the organic EL element 25, the p-type is used in the range where the drain current is Ia or less. The first drain current of the drive transistor 22 is used as the light emission current of the organic EL element, and the second drain current of the n-type drive transistor 23 can be passed as the light emission current of the organic EL element 25 in a range where the drain current is larger than Ia. It becomes.

Next, regarding the function of the conversion circuit 7 for causing the light emission current of the organic EL element 25 to flow continuously in accordance with the display gradation by the above-described data voltage ranges V _{L1 to} V _L2 and V _{H1 to} V _H2. explain. The conversion circuit 7 converts video data input from the outside into a converted data signal VT.

FIG. 6 is a graph showing the conversion characteristics of the conversion circuit according to the embodiment of the present invention. In the graph shown in the figure, the horizontal axis represents video data input to the conversion circuit 7 and the vertical axis represents the conversion data signal VT output from the conversion circuit 7. The video data is, for example, digital data for expressing a luminance of 256 gradations (0 to 255). The conversion characteristics of the graph are as follows: from the low gradation (0) to a predetermined intermediate gradation (for example, 127 gradation), the VT is monotonic in the range of V _{L1 to} V _{L2 as} the display gradation increases. is decreasing. Further, when the display gradation is from a predetermined intermediate gradation (for example, 128 gradation) to a high gradation, the VT monotonously increases in the range of V _{H1 to} V _{H2 as} the display gradation increases.

  The VT output from the conversion circuit 7 is input to the DA conversion circuit 41 of the data line driving circuit 4 and converted into a data voltage as an analog signal. In the present embodiment, the data line driving circuit 4 does not output the data voltage corresponding to the video data as it is, but converts the converted data signal that has been subjected to the predetermined conversion via the conversion circuit 7 into an analog signal. The resulting data voltage is supplied to the data line.

That is, when the data voltage corresponding to the converted data signal VT is in the range from V _{L2 to} V _L1 in the current-voltage characteristics of the p-type drive transistor 22, the conversion circuit 7 displays the display level of the video data corresponding to the range. The video data is converted into the converted data signal VT so that the data voltage decreases as the tone increases. On the other hand, when the data voltage corresponding to the converted data signal VT is in the range of V _H1 or more in the current-voltage characteristics of the n-type drive transistor 23, the data voltage increases as the display gradation of the video data corresponding to the range increases. Thus, the video data is converted into a converted data signal VT.

  The organic EL display panel 1 stores the above-described conversion characteristic table in, for example, a built-in memory. The conversion circuit 7 reads a conversion characteristic table from the memory and converts the video data into a conversion data signal using the table.

  According to this aspect, even when the organic EL element is driven using two drive transistors whose polarities are inverted from each other, the data voltage is in a range corresponding to the converted data signal obtained by converting the video data. Accordingly, a data voltage corresponding to the entire area from the minimum value to the maximum value of the video data can be generated.

As a result, the data voltage corresponding to the converted data signal VT is in the range from V _{L2 to} V _L1 in the current-voltage characteristic of the p-type drive transistor 22 and V _H1 in the current-voltage characteristic of the n-type drive transistor 23. Although the control for increasing / decreasing the conversion data signal corresponding to the video data is different in the above range, even when the organic EL element 25 is driven by using two drive transistors whose polarities are reversed from each other. The data voltage corresponding to the entire area from the minimum value to the maximum value of the video data can be generated.

  Hereinafter, the driving method of the organic EL display panel and the flow of various signals from when the video signal is input to the organic EL display panel of the present invention until the organic EL display panel performs a display operation will be described.

  FIG. 7A is a diagram showing the flow of various signals in the organic EL display panel according to the embodiment of the present invention. The video signal is composed of a synchronization signal and video data.

  The synchronization signal includes a vertical synchronization signal V, a horizontal synchronization signal H, and a DE (Display Enable) signal. These synchronization signals are input to the control circuit 2. The control circuit 2 receives the synchronization signal and outputs a start pulse signal to the scanning line driving circuit 3 to control the output timing of the scanning signal SCAN output from the scanning line driving circuit 3, and the data line driving circuit By outputting a synchronization signal to 4, the control for synchronizing the timing of supplying the data voltage output from the data line driving circuit 4 and the output timing of the scanning signal SCAN is performed.

  The video data is a digital luminance information signal for causing the organic EL element 25 of each light emitting pixel 6 </ b> A to emit light, and is input to the conversion circuit 7. The conversion circuit 7 converts the video data into a conversion data signal VT and outputs the converted data signal VT to the data line driving circuit 4 as in the conversion characteristics shown in FIG. The data line driving circuit 4 converts the digital conversion data signal VT into an analog data voltage by the built-in DA conversion circuit 41 and outputs it to the light emitting pixel 6A.

  FIG. 7B is a drive timing chart of the organic EL display panel according to the embodiment of the present invention. In the figure, in order from the top, the vertical synchronization signal V, the horizontal synchronization signal H, the DE signal, the video data, the converted data signal VT, the start pulse signal, the first row scanning signal SCAN_1, the second row scanning signal SCAN_2, The scanning signal SCAN_3 on the third row and the scanning signal SCAN_E on the last row are displayed in time series.

  First, the writing timing of one frame is determined by the vertical synchronizing signal V, and the writing timing to each light emitting pixel row is determined by the horizontal synchronizing signal H.

  Next, the scan signal SCAN is set to the high level sequentially in accordance with the start pulse signal, and the data voltage converted from the converted data signal VT in synchronization with the DE signal is output to the data line.

  Hereinafter, a method for driving an organic EL display panel according to an embodiment of the present invention will be described.

  FIG. 8 is a diagram showing the relationship of the operation flow of each circuit included in the organic EL display panel according to the embodiment of the present invention. FIG. 2 shows operations mainly including the control circuit 2, the scanning line driving circuit 3, the data line driving circuit 4, and the conversion circuit 7 included in the organic EL display panel 1 and the relationship between these operations.

  First, a video signal is input from the outside, and the organic EL display panel 1 inputs video data constituting the video signal to the conversion circuit 7 (S01), and inputs a synchronization signal to the control circuit 2 (S21).

  Next, the conversion circuit 7 converts the input video data into a converted data signal VT based on the conversion characteristics shown in FIG. 6 (S02). Then, the conversion circuit 7 outputs the converted conversion data signal VT to the data line driving circuit 4 (S03).

  On the other hand, the control circuit 2 to which the synchronization signal is input generates a start pulse signal from the DE signal that constitutes the input synchronization signal (S22).

  Next, the control circuit 2 outputs the DE signal to the data line driving circuit 4 and outputs the generated start pulse signal to the scanning line driving circuit 3 (S23).

  Next, the data line drive circuit 4 to which the DE signal is input converts the converted data signal VT output from the conversion circuit 7 into the data voltage Vdata by the built-in DA conversion circuit 41 (S11).

  Next, the data line driving circuit 4 sets the DA-converted data voltage in each data driver in the scanning order for each data line in order from the converted data signal VT synchronized with the DE signal (S12).

  On the other hand, the scanning line driving circuit 3 to which the start pulse signal is input generates a SCAN signal by the start pulse signal (S31).

  Next, the scanning line driving circuit 3 outputs the generated scanning signal SCAN for each scanning line (S32).

  The data line driving circuit 4 outputs the data voltage of the light emitting pixels connected to the scanning line that is at the high level by the scanning signal SCAN output from the scanning line driving circuit 3 (S13).

  Finally, the scanning line driving circuit 3 sets the scanning line that has been set to the high level in step S13 to the low level (S33).

  Hereinafter, a circuit operation of the light emitting pixel to which the scanning signal SCAN is input from the scanning line driving circuit 3 and the data voltage Vdata is input from the data line driving circuit 4 will be described.

  FIG. 9 is an operation flowchart of the light-emitting pixel circuit according to the embodiment of the present invention.

  First, the scanning line 11 is set to a high level by the scanning signal SCAN, and the selection transistor 21 of the light emitting pixel 6A is turned on (S41).

  Next, the data voltage of the light emitting pixel 6A is output from the data line driving circuit 4 to the data line 12 (S42).

  Through steps S41 and S42, a voltage corresponding to the data voltage is held in the capacitor 24 of the light emitting pixel 6A (S43).

  Next, the scanning line 11 is set to a low level by the scanning signal SCAN, and the selection transistor 21 of the light emitting pixel 6A is turned off (S44).

  Next, the p-type drive transistor 22 or the n-type drive transistor 23 is automatically turned on according to the magnitude of the applied data voltage (S45).

When the p-type drive transistor 22 is turned on in step S45, the first drain current flows from the first power supply line 14 to the organic EL element 25 through the p-type drive transistor 22 using the low voltage V _DD2 as the power supply voltage. (S47). On the other hand, when the n-type drive transistor 23 is turned on in step S45, the second drain current is supplied from the second power line 13 through the n-type drive transistor 23 using the high voltage V _DD1 as the power supply voltage. (S46).

  By step S46 or step S47, the organic EL element 25 emits light corresponding to the data voltage.

  FIG. 10 is an example of a driving timing chart for explaining in detail the driving operation of the organic EL display panel according to the embodiment of the present invention. The drive timing chart shown in the same figure is an excerpt of 4 horizontal periods of 4 pixels of the same data line in the drive timing chart shown in FIG. 7B, and specific data voltage values are set. The video data corresponding to the first to fourth lines are D1 to D4, respectively. The converted data signal VT and the data voltage corresponding to D1 to D4 are V1 to V4, respectively. In addition, drain currents flowing through the organic EL element 25 by the data voltages V1 to V4 are Id1 to Id4, respectively.

  Each of the video data D1 to D4 is converted into a converted data signal VT and a data voltage according to the conversion characteristics shown in FIG.

  FIG. 11 is a graph showing an example of the conversion characteristics of the conversion circuit according to the embodiment of the present invention. As shown in the figure, the video data D1 to D4 have progressively higher gradations from low gradation D1 to high gradation D4. D1 and D2 are converted into V1 and V2, respectively, using a conversion characteristic region in which the data voltage becomes lower as the video data becomes higher gradation. On the other hand, D3 and D4 are converted into V3 and V4, respectively, using a conversion characteristic region in which the data voltage increases as the video data becomes higher gradation.

  FIG. 12 is a diagram illustrating a circuit state of the light emitting pixels in the adjacent row according to the embodiment of the present invention. This figure shows a path through which a drain current flows when the data voltages V1 to V4 corresponding to the video data D1 to D4 described above are written to the first row of light emitting pixels to the fourth row of light emitting pixels, respectively. Has been.

  FIG. 13 is a graph showing an example of current-voltage characteristics of two drive transistors according to the embodiment of the present invention. The figure shows the current-voltage conversion characteristics of a light-emitting pixel realized by two drive transistors. In addition, the magnitudes of the drain currents Id1 to Id4 when the above-described data voltages V1 to V4 are written to the first to fourth rows of light emitting pixels are shown.

The graphs shown in FIGS. 11 to 13 show that low gradation video data D1 and D2 are converted into V1 and V2 by the conversion circuit 7, respectively, and V1 and V2 are in the range of V _{L2 to} V _L1. As shown, the first drain currents Id1 and Id2 flow from the p-type drive transistor 22 to the organic EL element 25 using the low voltage V _DD2 as a power supply voltage. Further, the video data D3 and D4 of the high gradation, respectively, are converted by the conversion circuit 7 in V3 and V4, n-type high voltage _{V DD1} as the power supply voltage since the V3 and V4 are in the range of _V H1 _{~V H2} It shows that the second drain currents Id3 and Id4 flow from the driving transistor 23 to the organic EL element 25, respectively.

  Returning to FIG. 10 again, the drive timing chart will be described. The video data D1 to D4 are converted into converted data signals and data voltages V1 to V4, respectively, and the converted data voltages V1 to V4 are synchronized with the scanning signals SCAN1 to SCAN4 of the first to fourth rows in each row. The drain currents Id1 to Id4 are generated in each light emitting pixel after the completion of the writing operation, and the organic EL element 25 emits light. With the above operation, power consumption P1 to P4 generated in the light emitting pixels in the first to fourth rows in one frame period is expressed as follows.

P1 = Id1 × V _DD2 (Formula 1)
P2 = Id2 × V _DD2 (Formula 2)
P3 = Id3 × V _DD1 (Formula 3)
P4 = Id4 × V _DD1 (Formula 4)

According to the above formulas 1 to 4, the first power supply line 14 to which the low voltage V _DD2 is applied is used in the display operation for the low gradation video data D1 and D2. Here, in the case of a conventional circuit configuration in which a drain current corresponding to video data of all gradations is passed by one drive transistor, the second power supply line 13 to which the high voltage V _DD1 is applied is always used. become. When both are compared, low gradation image data D1 and D2 are displayed when two drive transistors are arranged and the power supply line is properly used according to the display gradation as in the organic EL display panel 1 of the present invention. The overall power consumption of the panel can be reduced in that the power consumption is reduced.

  Although the embodiment has been described above, the organic EL display panel according to the present invention is not limited to the above-described embodiment. Another embodiment realized by combining arbitrary constituent elements in the above-described embodiment, and modifications obtained by applying various modifications conceivable by those skilled in the art to the above-described embodiment without departing from the gist of the present invention. Examples and organic EL display devices incorporating the organic EL display panel according to the present invention are also included in the present invention.

  For example, in the above embodiment, the source electrode or drain electrode of the two drive transistors is connected to the anode electrode of the organic EL element 25, and the two drive transistors are arranged on the higher potential side than the organic EL element 25. However, the present invention is not limited to this configuration. Hereinafter, modifications of the circuit configuration of the light emitting pixel 6A shown in the above embodiment will be described.

  FIG. 14 is a circuit diagram of a luminescent pixel showing a modification according to the embodiment of the present invention. In the light emitting pixel 6B shown in the figure, the cathode electrode of the organic EL element 45 and the source electrode or drain electrode of the two drive transistors are connected, and the two drive transistors are on the lower potential side than the organic EL element 45. The difference from the light emitting pixel 6 </ b> A shown in the embodiment is only in that the configuration arranged in FIG.

  The organic EL display panel including the light emitting pixel 6B described in FIG. 14 has the same effect as the organic EL display panel 1 according to the above-described embodiment. Hereinafter, the same points as the configuration of the light emitting pixel 6A will not be described, and different points will be mainly described.

  The light emitting pixel 6B illustrated in FIG. 14 includes a selection transistor 21, an n-type drive transistor 42, a p-type drive transistor 43, a capacitor 24, and an organic EL element 45. A data line 12 is arranged for each light emitting pixel column, and a scanning line 11 is arranged for each light emitting pixel row.

Further, the first power supply line 34, the second power supply line 33, the reference power supply line 35, and the reference power supply line 16 are arranged for all the light emitting pixels 6B. The first power supply line 34, the second power supply line 33, the reference power supply line 15, and the reference power supply line 16 are also connected to other light emitting pixels and are connected to the power supply circuit 5. Further, the high voltage _VEE2 set to the first power supply line 34 is set higher than the low voltage _VEE1 set to the second power supply line 33, and both the second power supply line 33 and the first power supply line 34 are set. The potential is set lower than that of the reference power line.

  The selection transistor 21 is a switching transistor in which the gate electrode is connected to the scanning line 11 and one of the source electrode and the drain electrode is connected to the gate electrodes of the n-type driving transistor 42 and the p-type driving transistor 43.

  The n-type drive transistor 42 has a gate electrode connected to the first electrode of the capacitor 24, a drain electrode connected to the cathode electrode of the organic EL element 45, and a source electrode connected to the first power supply line 34. With the above connection relationship, the n-type drive transistor 42 supplies the first drain current to the organic EL element 45 in accordance with the voltage held in the capacitor 24 to cause the organic EL element 45 to emit light. The n-type drive transistor 42 is composed of an n-type thin film transistor (n-type TFT). Here, in the present modification, the first drain current is a current that flows from the reference power supply line 35 to the first power supply line 34 via the n-type drive transistor 42.

  The p-type drive transistor 43 has a gate electrode connected to the first electrode of the capacitor 24, a source electrode connected to the cathode electrode of the organic EL element 45, and a drain electrode connected to the second power supply line 33. With the above connection relationship, the p-type drive transistor 43 supplies the second drain current to the organic EL element 45 according to the voltage held in the capacitor 24 to cause the organic EL element 45 to emit light. The p-type drive transistor 43 is composed of a p-type thin film transistor (p-type TFT). Here, in the present modification, the second drain current is a current that flows from the reference power supply line 35 to the second power supply line 33 via the p-type drive transistor 43.

  The organic EL element 45 is a light emitting element having a cathode electrode connected to the drain electrode of the n-type drive transistor 42 and the source electrode of the p-type drive transistor 43, and an anode electrode connected to the reference power supply line 35. Due to the above connection relationship, the organic EL element 45 emits light when the first drain current of the n-type drive transistor 42 or the second drain current of the p-type drive transistor 43 flows.

  The capacitor 24 has a first electrode connected to the gate electrodes of the n-type drive transistor 42 and the p-type drive transistor 43, and a second electrode connected to the reference power supply line 16 to hold a voltage corresponding to the data voltage.

Here, the first drain current supplied from the n-type drive transistor 42 and the second drain current supplied from the p-type drive transistor 43 are selectively set using a predetermined current value in the current-voltage characteristics of the organic EL element 25 as a threshold value. Are set to flow through the organic EL element 45. That is, in each display gradation, one of the first drain current and the second drain current flows through the organic EL element 45, so that one of the drain currents becomes the light emission current of the organic EL element 25. In the light emitting pixel 6B, for example, in the low light emission current region, the n-type drive transistor 42 is turned on to flow the first drain current as the light emission current. In the high light emission current region, the p-type drive transistor 43 is turned on and the second drain current flows as the light emission current. Therefore, in the low light emission current region, the first drain current flows through the organic EL element 45 from the reference power supply line 35 to the second power supply line 33 where the low voltage _VEE1 is set. Therefore, in the display operation in the low light emission current region, the power consumption can be reduced as compared with the case where the drain current is supplied to the first power supply line 34.

  That is, in the light emitting pixel 6B, the number of driving transistors is increased by one as compared with a normal light emitting pixel circuit, but without adding a switching circuit between the first power supply line 34 and the second power supply line 33, By increasing the number of drive transistors by one without providing a data line and a select transistor for every two drive transistors, the first power supply line 34 and the second power supply line 33 can be changed according to the data voltage. Can be used properly. As a result, an energy-saving pixel circuit with low power consumption can be realized with a simple configuration without significantly increasing the circuit elements of the light-emitting pixels.

FIG. 15 is a graph showing current-voltage characteristics of two drive transistors included in a light emitting pixel according to a modification according to the embodiment of the present invention. Here, in this modification, the first gate voltage value is _VL2 , the second gate voltage value is _VH1 , the third gate voltage value is _VH0 , and the fourth gate voltage value. Is V _L1 .

The n-type drive transistor 42 is a data voltage in which the first gate voltage value V _L2 when the current Ia in the current-voltage characteristic of the organic EL element shown in FIG. The current-voltage characteristic is such that the gate voltage for flowing the first drain current decreases as the first drain current becomes smaller than the current Ia. In other words, it has a current-voltage characteristic in which the first drain current increases as the gate voltage increases.

On the other hand, the p-type drive transistor 43 has a third gate voltage value V _H1 corresponding to the minimum current value Imin that flows through the organic EL element 45 when the current Ia flows as the second drain current. _The voltage value is smaller than _H0 , and the current-voltage characteristic is such that the gate voltage for flowing the second drain current decreases as the second drain current becomes larger than the current Ia. In other words, it has a current-voltage characteristic in which the second drain current decreases as the gate voltage increases. Here, the current value Imin is a current value on the horizontal axis in the current-voltage characteristic shown in FIG. 15, and a current smaller than the current value can be ignored as a light emission current.

Note that the fourth gate voltage value V _L1 corresponding to the minimum current value Imin in the current-voltage characteristics of the n-type drive transistor 42 is preferably set larger than the third gate voltage value V _H0 .

  As a result, the range of the gate voltage for flowing the first drain current by the n-type drive transistor 42 and the range of the gate voltage for flowing the second drain current by the p-type drive transistor 43 do not overlap and are completely separated. The As a result, the organic EL element 45 is caused to emit light by the drain current supplied from only one of the driving transistors at all data voltages without adding a switching circuit between the high voltage power line and the low voltage power line. It becomes possible.

  For example, the organic EL display panel according to the present invention is built in a thin flat TV as shown in FIG. By incorporating the organic EL display panel according to the present invention, a thin flat TV capable of displaying images with low power consumption and high accuracy is realized.

  The present invention is particularly useful for an active organic EL flat panel display in which the luminance is varied by controlling the light emission intensity of the pixel by the pixel signal current.

DESCRIPTION OF SYMBOLS 1 Organic EL display panel 2 Control circuit 3 Scan line drive circuit 4 Data line drive circuit 5 Power supply circuit 6 Display part 6A, 6B, 100A Light emission pixel 7 Conversion circuit 11, 111 Scan line 12, 112 Data line 13, 33 2nd Power supply line 14, 34 First power supply line 15, 35, 115 Reference power supply line 16 Reference power supply line 21, 121a, 121b Select transistor 22, 43, 122 P-type drive transistor 23, 42 N-type drive transistor 24 Capacitors 25, 45, 125 Organic EL element 41 DA conversion circuit 113 High luminance power line 114 Low luminance power line 123 Switching transistor 124a, 124b Retention capacitance element 126 Diode

  The present invention relates to an organic EL display panel and a driving method thereof, and more particularly to an organic EL display panel using an active matrix driving circuit and a driving method thereof.

  As a display panel using a current-driven light emitting element, a display panel using an organic electroluminescence (EL) element is known. The organic EL display panel using the organic EL element that emits light does not require the backlight necessary for the liquid crystal display panel, and is optimal for thinning the device. Moreover, since there is no restriction | limiting also in a viewing angle, utilization as a next-generation display panel is anticipated. Further, the organic EL element used in the organic EL display panel is different from the liquid crystal cell being controlled by the voltage applied thereto, in that the luminance of each light emitting element is controlled by the current value flowing therethrough.

  In an organic EL display panel, organic EL elements constituting pixels are usually arranged in a matrix. An organic EL element is provided at the intersection of a plurality of row electrodes (scanning lines) and a plurality of column electrodes (data lines), and a voltage corresponding to a data signal is applied between the selected row electrodes and the plurality of column electrodes. A device for driving an organic EL element is called a passive matrix type organic EL display.

  On the other hand, a switching thin film transistor (TFT) is provided at the intersection of a plurality of scanning lines and a plurality of data lines, the gate of the driving TFT is connected to the switching TFT, and the switching TFT is turned on through the selected scanning line. Then, a data signal is input from the signal line to the driving TFT. A device in which the organic EL element is driven by the driving TFT is called an active matrix type organic EL display panel.

  The active matrix organic EL display panel differs from the passive matrix organic EL display panel in which the organic EL element connected thereto emits light only during the period when each row electrode (scanning line) is selected. Since the organic EL element can emit light until the selection), the luminance of the display is not reduced even if the number of scanning lines is increased. In this respect, the active matrix driving method is advantageous in realizing a large screen and a high-definition display panel.

  On the other hand, an organic EL display panel using a current-driven organic EL element emits light when a current flows through the organic EL element of each pixel, so that it is compared with a liquid crystal element that is a voltage-driven element. Therefore, the power consumption of the display panel tends to increase. In particular, the power consumption of the display panel increases with an increase in screen size and resolution.

  Patent Document 1 discloses a circuit configuration for reducing power consumption of a pixel portion in an active matrix organic EL display device.

  FIG. 17 is a circuit diagram illustrating an example of a specific circuit configuration of a pixel circuit included in the organic EL display device described in Patent Document 1. As shown in the figure, the light emitting pixel 100A includes a selection transistor 121b for writing the voltage of the data line 112 to the storage capacitor element 124b when the light emitting pixel 100A is selected by the scanning signal from the scanning line 111. , The storage capacitor element 124b, the p-type drive transistor 122 that causes the drive current corresponding to the storage voltage of the storage capacitor element 124b to flow from the high luminance power line 113 or the low luminance power line 114 to the reference power line 115, and the driving And an organic EL element 125 that emits light when a current flows. The above pixel configuration is a configuration provided in a normal pixel circuit.

  Further, the light emitting pixel 100A includes a switching transistor 123 for turning on / off the high-brightness power supply voltage from the high-brightness power supply line 113 and a diode 126 for turning on / off the low-brightness power supply voltage from the low-brightness power supply line 114. A storage capacitor element 124a having one end connected to the high-brightness power supply line 113 and the other end connected to the gate of the switching transistor 123; and a gate connected to the scanning line 111; A selection transistor 121a that inputs a control signal VELS to the gate of the switching transistor 123 when 100A is selected. The source of the switching transistor 123 and the cathode of the diode 126 are commonly connected, and the source of the p-type drive transistor 122 is connected to the common connection point.

  The switching transistor 123, the selection transistor 121 a, the storage capacitor element 124 a, and the diode 126 described above use either a high-brightness power supply voltage or a low-brightness power supply voltage as a pixel power supply voltage supplied to the p-type drive transistor 122. A power supply voltage switching means for switching whether or not to perform is configured.

  In the above circuit configuration, when the power supply voltage for high luminance is selected, the scanning signal and the control signal VELS are simultaneously at the high level during the writing period. In this case, the switching transistor 123 is turned on, and the power supply voltage for high brightness is supplied to the source of the p-type drive transistor 122. At this time, since the anode potential becomes the low-brightness power supply voltage and the cathode potential becomes the high-brightness power supply voltage, the diode 126 is in a reverse bias state and is automatically turned off. The power supply voltage is cut off.

  On the other hand, when the power supply voltage for low luminance is selected, only the scanning signal becomes high level during the writing period, and the control signal VELS maintains low level. In this case, the switching transistor 123 is turned off, and the power supply voltage from the high luminance power supply line 113 is cut off. At this time, the diode 126 is forward biased and turned on, and the low-brightness power supply voltage is supplied to the source of the p-type drive transistor 122.

  As described above, in the circuit configuration shown in FIG. 17, the diode 126 is turned on / off by turning on / off the switching transistor 123 by the control signal VELS.

  Here, the voltage level of the control signal VELS is determined as follows by the scanning line driving circuit to which the scanning line 111 is connected. For example, when all the display gradations are expressed by 256 gradations, when the gradation signal value of the light emitting pixel 100A belongs to the high gradation side when the 128 gradation values are used as the reference value, the high luminance is obtained. The control signal VELS is set to a high level so as to select a power supply voltage for low power, and when belonging to the low gradation side, the control signal VELS is set to a low level so as to select a power supply voltage for low luminance.

  With the above configuration, the organic EL display device described in Patent Document 1 is provided with a high-brightness power supply voltage and a low-brightness power supply voltage, and individually controls the pixel voltage for each pixel circuit by the control signal VELS. As a result, a circuit configuration is provided in which a reduction in image quality is surely prevented and power consumption is also reduced.

JP 2008-89726 A

  However, in the organic EL display device described in Patent Document 1, in order to select a low power supply voltage as a pixel power supply used at the time of low gradation display, in addition to a circuit configuration essential for a normal pixel circuit, power supply voltage switching means As described above, a selection transistor 121a, a storage capacitor element 124a, and a diode 126 are required for each light emitting pixel. Further, a control line for applying the control signal VELS to the gate of the switching transistor 123 must be provided separately from the scanning line driving circuit. These circuit components and wiring increase the circuit scale of the pixel circuit, which is inconvenient for high definition display panels.

  Further, the scanning line driving circuit has to switch the voltage level of the control signal VELS for each light emitting pixel, which increases the load of switching the voltage of the output signal from the driving circuit.

  In view of the above problems, the present invention realizes low power consumption with a simple pixel circuit configuration without significantly increasing the number of elements of the pixel circuit even when the light-emitting pixel is miniaturized and high-definition progresses. An object of the present invention is to provide an organic EL display panel and a driving method thereof.

  In order to achieve the above object, an organic EL display panel according to an aspect of the present invention includes an organic EL element, a capacitor having a first electrode and a second electrode, and holding a voltage corresponding to a data voltage; A gate electrode is connected to the first electrode of the capacitor, a drain electrode is connected to the anode electrode of the organic EL element, and a first drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. Thus, the p-type first driving transistor for causing the organic EL element to emit light, the gate electrode is connected to the first electrode of the capacitor, the source electrode is connected to the anode electrode of the organic EL element, and held by the capacitor In addition, an n-type second drive transistor that emits light from the organic EL element by supplying a second drain current corresponding to the voltage to the organic EL element. A data line for supplying the data voltage, a switching transistor for holding the voltage in the capacitor by switching conduction and non-conduction between the data line and the capacitor, and the first drive transistor A first power supply line for applying a first power supply voltage to the source electrode of the second drive transistor, and a second power supply line for applying a second power supply voltage higher than the first power supply voltage to the drain electrode of the second drive transistor, In the one drive transistor, a first gate voltage value corresponding to a predetermined current value in the current-voltage characteristic of the organic EL element is a minimum voltage in the data voltage, and the first drain current is smaller than the predetermined current value. It is a transistor having a current-voltage characteristic such that the gate voltage for flowing the first drain current increases. In the second drive transistor, the second gate voltage value corresponding to the predetermined current value is a voltage value larger than a third gate voltage value corresponding to the minimum current value passed through the organic EL element, The transistor has a current-voltage characteristic such that a gate voltage for allowing the second drain current to flow increases as the second drain current becomes larger than the predetermined current value.

  According to the organic EL display panel and the driving method thereof of the present invention, two drive transistors are required for each light-emitting pixel in order to reduce power consumption, but a switching circuit between a high voltage power line and a low voltage power line. Without increasing the number of drive transistors, and by increasing the number of drive transistors by one without arranging two data lines and two select transistors corresponding to the two drive transistors, The high voltage power line and the low voltage power line are automatically selected. As a result, an energy-saving pixel circuit can be realized with a simple configuration without significantly increasing the circuit elements of the light emitting pixels.

FIG. 1 is a functional block diagram of an organic EL display panel according to an embodiment of the present invention. FIG. 2 is a circuit diagram of the light emitting pixel according to the embodiment of the present invention. FIG. 3 is a graph schematically showing current-voltage characteristics of the organic EL element. FIG. 4 is a graph showing current-voltage characteristics of two drive transistors according to the embodiment of the present invention. FIG. 5A is a graph showing current-voltage characteristics of the p-type drive transistor according to the exemplary embodiment of the present invention. FIG. 5B is a graph showing current-voltage characteristics of the n-type drive transistor according to the exemplary embodiment of the present invention. FIG. 6 is a graph showing the conversion characteristics of the conversion circuit according to the embodiment of the present invention. FIG. 7A is a diagram showing the flow of various signals in the organic EL display panel according to the embodiment of the present invention. FIG. 7B is a drive timing chart of the organic EL display panel according to the embodiment of the present invention. FIG. 8 is a diagram showing the relationship of the operation flow of each circuit included in the organic EL display panel according to the embodiment of the present invention. FIG. 9 is an operation flowchart of the light-emitting pixel circuit according to the embodiment of the present invention. FIG. 10 is an example of a driving timing chart for explaining in detail the driving operation of the organic EL display panel according to the embodiment of the present invention. FIG. 11 is a graph showing an example of the conversion characteristics of the conversion circuit according to the embodiment of the present invention. FIG. 12 is a diagram illustrating a circuit state of the light emitting pixels in the adjacent row according to the embodiment of the present invention. FIG. 13 is a graph showing an example of current-voltage characteristics of two drive transistors according to the embodiment of the present invention. FIG. 14 is a circuit diagram of a luminescent pixel showing a modification according to the embodiment of the present invention. FIG. 15 is a graph showing current-voltage characteristics of two drive transistors included in a light emitting pixel according to a modification according to the embodiment of the present invention. FIG. 16 is an external view of a thin flat TV incorporating the organic EL display panel of the present invention. FIG. 17 is a circuit diagram illustrating an example of a specific circuit configuration of a pixel circuit included in the organic EL display device described in Patent Document 1.

  In order to achieve the above object, an organic EL display panel according to an aspect of the present invention includes an organic EL element, a capacitor having a first electrode and a second electrode, and holding a voltage corresponding to a data voltage; A gate electrode is connected to the first electrode of the capacitor, a drain electrode is connected to the anode electrode of the organic EL element, and a first drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. Thus, the p-type first driving transistor for causing the organic EL element to emit light, the gate electrode is connected to the first electrode of the capacitor, the source electrode is connected to the anode electrode of the organic EL element, and held by the capacitor In addition, an n-type second drive transistor that emits light from the organic EL element by supplying a second drain current corresponding to the voltage to the organic EL element. A data line for supplying the data voltage, a switching transistor for holding the voltage in the capacitor by switching conduction and non-conduction between the data line and the capacitor, and the first drive transistor A first power supply line for applying a first power supply voltage to the source electrode of the second drive transistor, and a second power supply line for applying a second power supply voltage higher than the first power supply voltage to the drain electrode of the second drive transistor, In the one drive transistor, a first gate voltage value corresponding to a predetermined current value in the current-voltage characteristic of the organic EL element is a minimum voltage in the data voltage, and the first drain current is smaller than the predetermined current value. It is a transistor having a current-voltage characteristic such that the gate voltage for flowing the first drain current increases. In the second drive transistor, the second gate voltage value corresponding to the predetermined current value is a voltage value larger than a third gate voltage value corresponding to the minimum current value passed through the organic EL element, The transistor has a current-voltage characteristic in which a gate voltage for flowing the second drain current increases as the second drain current becomes larger than the predetermined current value.

  According to this aspect, two power supply lines having different power supply voltages are provided, and the first power supply line and the second power supply line are selectively used according to the data voltage. Therefore, the high power supply voltage prepared as the maximum value for any data voltage is not supplied, but only when the data voltage requires a high power supply voltage for light emission with accurate brightness. The power supply voltage will be used. As a result, power consumption can be greatly reduced as compared with the case where a high power supply voltage is supplied to any data voltage.

  In addition, according to this aspect, two power supply lines are provided, and when the first power supply line and the second power supply line are selected according to the data voltage, the p-type first transistor is used as a drive transistor for driving the organic EL element. There are provided drive transistors having opposite polarities, that is, a drive transistor and an n-type second drive transistor. The source electrode of the p-type first drive transistor is connected to the first power supply line, and the drain electrode of the n-type second drive transistor is connected to the second power supply line.

  In addition, the first drive transistor has a minimum gate voltage when a predetermined current value in the current-voltage characteristic of the organic EL element flows as the first drain current, and the first drain current is greater than the predetermined current value. The transistor has current-voltage characteristics such that the gate voltage value for flowing the first drain current increases as the value decreases. On the other hand, in the second drive transistor, the gate voltage value when the predetermined current value flows as the second drain current is a voltage value larger than the gate voltage value corresponding to the minimum current value flowing through the organic EL element. The transistor has current-voltage characteristics such that the gate voltage value for flowing the second drain current increases as the drain current becomes larger than the predetermined current value. Note that the minimum current value flowing through the organic EL element is a current value when the forward current starts to flow exceeding the threshold voltage in the organic EL element having diode characteristics, and is a current at which the organic EL element starts to emit light. is there.

  As a result, although the number of drive transistors increases by one, a data line and a switching transistor are provided for each of the two drive transistors without adding a switching circuit between the first power supply line and the second power supply line. Without increasing the number of driving transistors, the first power supply line and the second power supply line can be selectively used according to the data voltage. As a result, an energy-saving pixel circuit with low power consumption can be realized with a simple configuration without significantly increasing the circuit elements of the light-emitting pixels.

  In the organic EL display panel according to an aspect of the present invention, the fourth gate voltage value corresponding to the minimum current value flowing through the organic EL element in the current-voltage characteristics of the first drive transistor is the third voltage. The gate voltage is preferably smaller than

  According to this aspect, the range of the gate voltage for flowing the first drain current by the p-type first drive transistor and the range of the gate voltage for flowing the second drain current by the n-type second drive transistor overlap. Rather, it is completely separated. As a result, the organic EL element can be caused to emit light by the drain current supplied from only one of the driving transistors at all data voltages without adding a switching circuit between the high voltage power line and the low voltage power line. Is possible.

  The organic EL display panel according to an aspect of the present invention further includes a conversion circuit that converts video data into a conversion data signal, and a DA conversion that converts the conversion data signal input from the conversion circuit into the data voltage. It is preferable that the data line driving circuit includes a circuit and supplies the data voltage to the data line.

  In this aspect, the data line driving circuit does not input the data voltage corresponding to the video data as it is, but converts the data voltage obtained by analog conversion of the converted data signal that has undergone predetermined conversion via the conversion circuit. Supply to the data line.

  Further, in the organic EL display panel according to one aspect of the present invention, the conversion circuit has the first gate voltage value in the current-voltage characteristic of the first drive transistor, wherein the data voltage corresponding to the converted data signal is To the fourth gate voltage value, the converted data signal is converted so that the converted data voltage becomes smaller as the display gradation of the video data corresponding to the range increases, and the converted data signal When the data voltage corresponding to the range is equal to or higher than the second gate voltage value in the current-voltage characteristic of the second driving transistor, the converted video data corresponding to the range increases as the display gradation of the video data increases. It is preferable to convert the converted data signal so that the data voltage is increased.

  According to this aspect, even when the organic EL element is driven using two drive transistors whose polarities are inverted from each other, the data voltage is in a range corresponding to the converted data signal obtained by converting the video data. Accordingly, a data voltage corresponding to the entire area from the minimum value to the maximum value of the video data can be generated.

  As a result, the data voltage corresponding to the converted data signal corresponds to the minimum current value that flows from the first gate voltage value corresponding to the predetermined current value to the organic EL element in the current-voltage characteristics of the first drive transistor. Corresponding to video data in the range up to the fourth gate voltage value and in the current-voltage characteristic of the second drive transistor in the range equal to or higher than the second gate voltage value corresponding to the predetermined current value. Although the control for increasing / decreasing the conversion data signal to be performed is different, the entire region from the minimum value to the maximum value of the video data is used even when the organic EL element is driven by using two drive transistors having opposite polarities. The data voltage corresponding to can be generated.

  The organic EL display panel according to an aspect of the present invention further includes a scanning line driving circuit that outputs a scanning signal for controlling conduction and non-conduction of the switching transistor to the switching transistor through the scanning line. Is preferred.

  According to this aspect, the supply timing of the data voltage to the light emitting pixel is determined by the scanning signal output from the scanning line driving circuit to the switching transistor via the scanning line.

  In the organic EL display panel according to one embodiment of the present invention, pixel circuits including the organic EL element, the capacitor, the first driving transistor, and the second driving transistor may be arranged in a matrix. .

  As a result, the number of drive transistors is increased by one in each pixel circuit, and the first power supply line and the second power supply line can be selectively used according to the data voltage. As a result, the display panel as a whole having light emitting pixels arranged in a matrix can be realized with a simple configuration without significantly increasing circuit elements.

  The organic EL display panel according to an aspect of the present invention further includes a control circuit for controlling the data line driving circuit and the scanning line driving circuit, and the control circuit is configured to control the matrix by the scanning line driving circuit. The switching circuit included in each pixel circuit in a certain line is ON-controlled, and the data voltage is supplied to each pixel circuit in the certain line via the data line by the data line driving circuit. You may perform control which synchronizes with a timing.

  According to this aspect, the supply timing of the data voltage from the data line driving circuit and the supply timing of the scanning signal from the scanning line driving circuit are synchronized in row order. Thereby, row sequential scanning of panel light emission is realized.

  Further, in the organic EL display panel according to one embodiment of the present invention, the data line driving circuit is configured such that each pixel circuit in one matrix-like line from the scanning line driving circuit is input by a synchronization signal from the control circuit. The data voltage may be supplied to the pixel circuits in the certain line via the data line in synchronization with the timing of outputting the scanning signal.

  According to this aspect, even when the conversion circuit is arranged in the preceding stage of the data line driving circuit and the conversion tendency of the data voltage is changed according to the video signal, the converted data voltage is synchronized with the scanning signal. It is possible to output from the line drive circuit.

  In addition, the present invention can be realized not only as an organic EL display panel including such characteristic means but also as an organic EL display device including the organic EL display panel.

  The present invention can be realized not only as an organic display panel having such characteristic means, but also as a method for driving an organic EL display panel using characteristic means included in the organic EL display panel as a step. Can be realized.

  In addition, an organic EL display panel according to one embodiment of the present invention includes an organic EL element, a first electrode and a second electrode, a capacitor holding a voltage corresponding to a data voltage, and a gate electrode of the capacitor. The organic EL element is connected to the first electrode, the drain electrode is connected to the cathode electrode of the organic EL element, and a first drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. An n-type first driving transistor that emits light, a gate electrode connected to the first electrode of the capacitor, a source electrode connected to a cathode electrode of the organic EL element, and according to the voltage held in the capacitor A p-type second drive transistor that emits light from the organic EL element by supplying a second drain current to the organic EL element; A data line for supplying the data, a switching transistor for holding the data voltage in the first electrode of the capacitor by switching between conduction and non-conduction between the data line and the capacitor, and A first power supply line for setting a first power supply voltage on the source electrode; and a second power supply line for setting a second power supply voltage lower than the first power supply voltage on the drain electrode of the second drive transistor, In the driving transistor, the first gate voltage value corresponding to the predetermined current value in the current-voltage characteristic of the organic EL element is the maximum voltage in the data voltage, and the first drain current is smaller than the predetermined current value. The transistor has a current-voltage characteristic such that the gate voltage for flowing the first drain current is small. In the second driving transistor, a second gate voltage value corresponding to the predetermined current value is smaller than a third gate voltage value corresponding to a minimum current value passed through the organic EL element, and The transistor may have a current-voltage characteristic such that the gate voltage for flowing the second drain current decreases as the 2-drain current becomes larger than the predetermined current value.

  According to this aspect, even in the circuit configuration in which the drive transistor is connected to the cathode side of the organic EL element, the same effect as the organic EL display panel having the circuit configuration in which the drive transistor is connected to the anode side of the organic EL element is obtained. Played.

(Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a functional block diagram of an organic EL display panel according to an embodiment of the present invention. The organic EL display panel 1 in FIG. 1 includes a control circuit 2, a scanning line driving circuit 3, a data line driving circuit 4, a power supply circuit 5, a display unit 6, and a conversion circuit 7.

  The display unit 6 includes a plurality of light emitting pixels 6A arranged in a matrix. The data voltage Vdata is supplied to the light emitting pixel 6A via a data line arranged for each light emitting pixel column. The scanning signal SCAN is supplied to the light emitting pixel 6A via a scanning line arranged for each light emitting pixel row.

  The scanning line driving circuit 3 drives the circuit elements included in the light emitting pixels 6A by sequentially outputting the scanning signals SCAN to the scanning lines arranged for each row. The scanning signal SCAN is a signal for switching between conduction and non-conduction of the switching transistor of the light emitting pixel 6A. Specifically, the scanning line driving circuit 3 supplies the scanning signal SCAN to the light emitting pixels 6 </ b> A in response to the input of the start pulse signal from the control circuit 2.

  The data line driving circuit 4 drives a circuit element of the light emitting pixel by outputting a data voltage based on the video signal to the data line arranged for each column. Specifically, the data line driving circuit 4 synchronizes with the timing at which the scanning signal is output from the scanning line driving circuit 3 to the light emitting pixels 6A in a row-sequential manner by the input of the synchronizing signal from the control circuit 2, and the data voltage is set. The light is supplied to the light emitting pixel 6A. The data line driving circuit 4 includes a DA (digital / analog) conversion circuit that converts a converted data signal that is a digital signal input from the conversion circuit 7 into a data voltage that is an analog signal.

  The control circuit 2 controls the output timing of the scanning signal SCAN output from the scanning line driving circuit 3. The control circuit 2 controls the timing for outputting the data voltage output from the data line driving circuit 4. Specifically, the timing at which the switching transistor of the light emitting pixel 6A is turned on is controlled by outputting a start pulse signal to the scanning line driving circuit 3 based on a video signal input from the outside. In addition, by outputting a synchronization signal to the data line driving circuit 4, control is performed to synchronize the timing for supplying the data voltage output from the data line driving circuit 4 and the output timing of the scanning signal SCAN.

  The power supply circuit 5 supplies a constant power supply voltage to all the light emitting pixels 6A via each power supply line.

  The conversion circuit 7 converts video data, which is luminance information of a video signal input from the outside, into a converted data signal. A specific conversion method will be described later with reference to FIG.

FIG. 2 is a circuit diagram of the light emitting pixel according to the embodiment of the present invention. The light emitting pixel 6 </ b> A shown in the figure includes a selection transistor 21, a p-type drive transistor 22, an n-type drive transistor 23, a capacitor 24, and an organic EL element 25. A data line 12 is arranged for each light emitting pixel column, and a scanning line 11 is arranged for each light emitting pixel row. Further, the first power supply line 14, the second power supply line 13, the reference power supply line 15, and the reference power supply line 16 are arranged for all the light emitting pixels 6A. The first power supply line 14, the second power supply line 13, the reference power supply line 15, and the reference power supply line 16 are also connected to other light emitting pixels, and are connected to the power supply circuit 5. Further, the high voltage V _DD1 set on the second power supply line 13 is set higher than the low voltage V _DD2 set on the first power supply line 14, and both the first power supply line 14 and the second power supply line 13 are set. The potential is set higher than that of the reference power line 15.

  The data line 12 is connected to the data line driving circuit 4 and connected to each light emitting pixel belonging to the pixel column including the light emitting pixel 6A. As a result, the data voltage Vdata that determines the light emission intensity is supplied to the light emitting pixel 6A via the data line 12.

  The scanning line 11 is connected to the scanning line driving circuit 3 and is connected to each light emitting pixel belonging to the pixel row including the light emitting pixel 6A. Accordingly, the scanning signal SCAN indicating the timing for writing the data voltage Vdata is supplied to the light emitting pixel 6A via the scanning line 11.

  The selection transistor 21 is a switching transistor in which the gate electrode is connected to the scanning line 11 and one of the source electrode and the drain electrode is connected to the gate electrodes of the p-type driving transistor 22 and the n-type driving transistor 23. The selection transistor 21 switches the conduction and non-conduction between the data line 12 and the capacitor 24 according to the scanning signal SCAN from the scanning line 11 to cause the capacitor 24 to hold a voltage corresponding to the data voltage. The selection transistor 21 is composed of, for example, an n-type thin film transistor (n-type TFT).

  The p-type drive transistor 22 has a gate electrode connected to the first electrode of the capacitor 24, a drain electrode connected to the anode electrode of the organic EL element 25, and a source electrode connected to the first power supply line 14. Due to the above connection relationship, the p-type drive transistor 22 supplies the first drain current to the organic EL element 25 in accordance with the voltage held in the capacitor 24 to cause the organic EL element 25 to emit light. The p-type drive transistor 22 is composed of a p-type thin film transistor (p-type TFT). Here, the first drain current is a current that flows from the first power supply line 14 to the reference power supply line 15 via the p-type drive transistor 22.

  The n-type drive transistor 23 has a gate electrode connected to the first electrode of the capacitor 24, a source electrode connected to the anode electrode of the organic EL element 25, and a drain electrode connected to the second power supply line 13. With the above connection relationship, the n-type drive transistor 23 supplies the second drain current to the organic EL element 25 according to the voltage held in the capacitor 24 to cause the organic EL element 25 to emit light. The n-type drive transistor 23 is composed of an n-type thin film transistor (n-type TFT). Here, the second drain current is a current that flows from the second power supply line 13 to the reference power supply line 15 via the n-type drive transistor 23.

  The organic EL element 25 is a light emitting element having an anode electrode connected to the drain electrode of the p-type drive transistor 22 and the source electrode of the n-type drive transistor 23, and a cathode electrode connected to the reference power supply line 15. Due to the above connection relationship, the organic EL element 25 emits light when the first drain current of the p-type drive transistor 22 or the second drain current of the n-type drive transistor 23 flows.

  The capacitor 24 has a first electrode connected to the gate electrodes of the p-type drive transistor 22 and the n-type drive transistor 23, and a second electrode connected to the reference power supply line 16, and holds a voltage corresponding to the data voltage. For example, after the selection transistor 21 is turned off, the gate-source voltage of the p-type drive transistor 22 and the n-type drive transistor 23 is stably maintained, and the first and second drain currents are stabilized. Have.

Here, the first drain current supplied from the p-type drive transistor 22 and the second drain current supplied from the n-type drive transistor 23 are selectively set with a predetermined current value in the current-voltage characteristics of the organic EL element 25 as a threshold value. Are set to flow through the organic EL element 25. That is, in each display gradation, one of the first drain current and the second drain current flows through the organic EL element 25, so that one of the drain currents becomes the light emission current of the organic EL element 25. In the light emitting pixel 6A, for example, in the low light emission current region, the p-type drive transistor 22 is turned on and the first drain current flows as the light emission current. In the high light emission current region, the n-type drive transistor 23 is turned on and the second drain current flows as the light emission current. For this reason, in the low light emission current region, the first drain current flows from the first power supply line 14 where the low voltage V _DD2 is set to the organic EL element 25. Therefore, in the display operation in the low light emission current region, the power consumption can be reduced as compared with the case where the drain current flows from the second power supply line 13.

  That is, in the light emitting pixel 6A according to the embodiment of the present invention, the number of driving transistors is increased by one as compared with a normal light emitting pixel circuit, but switching between the first power supply line 14 and the second power supply line 13 is performed. By increasing the number of driving transistors by one without increasing the number of circuits and without providing a data line and a selection transistor for every two driving transistors, the first power supply line can be selected according to the data voltage. 14 and the second power supply line 13 can be used properly. As a result, an energy-saving pixel circuit with low power consumption can be realized with a simple configuration without significantly increasing the circuit elements of the light-emitting pixels.

  Hereinafter, in the organic EL display panel 1 of the present invention, the first drain current and the second drain current are changed according to the display gradation without adding a switching circuit between the first power line 14 and the second power line 13. A configuration for realizing selection will be described.

  FIG. 3 is a graph schematically showing current-voltage characteristics of the organic EL element. In the figure, the horizontal axis represents the voltage applied between the anode and cathode of the organic EL element, and the vertical axis represents the forward current. As shown in the figure, the current-voltage characteristics of the organic EL element 25 are diode characteristics. When a voltage equal to or higher than a predetermined threshold voltage is applied between the anode and the cathode, a forward current starts to flow, and the current monotonously increases as the voltage increases.

  Here, in the organic EL display panel 1 according to the embodiment of the present invention, a predetermined current value Ia is defined in the current-voltage characteristics of the organic EL element 25. With the current Ia emitted from the organic EL element 25 as a boundary current, light is emitted to the organic EL element 25 via the second power supply line 13 and the n-type drive transistor 23 that supply a high power supply voltage in a current region larger than Ia. In the current region below Ia, a light emission current is supplied to the organic EL element 25 via the first power supply line 14 and the p-type drive transistor 22 that supply a low power supply voltage.

  Next, current-voltage characteristics of the p-type drive transistor 22 and the n-type drive transistor 23 for flowing either the first drain current or the second drain current to the organic EL element 25 using Ia as a threshold will be described.

FIG. 4 is a graph showing current-voltage characteristics of two drive transistors according to the embodiment of the present invention. In the figure, the horizontal axis represents the data voltage Vdata, that is, the voltage applied to the gate electrode of the driving transistor, and the vertical axis represents the drain current Id of the driving transistor. The first gate voltage value is V _L2 , the second gate voltage value is V _H1 , the third gate voltage value is V _H0 , and the fourth gate voltage value is V _L1 .

The p-type driving transistor 22 is data in which the first gate voltage value V _L2 when the current Ia in the current-voltage characteristic of the organic EL element 25 shown in FIG. The current-voltage characteristic is such that the gate voltage for allowing the first drain current to flow increases as the first drain current becomes smaller than the current Ia. In other words, it has a current-voltage characteristic in which the first drain current decreases as the gate voltage increases.

On the other hand, the n-type drive transistor 23 has a third gate voltage value V _H1 corresponding to the minimum current value Imin that flows through the organic EL element 25 when the current Ia flows as the second drain current. _The voltage value is higher than _H0 , and the current-voltage characteristic is such that the gate voltage for flowing the second drain current increases as the second drain current becomes larger than the current Ia. In other words, it has a current-voltage characteristic in which the second drain current increases as the gate voltage increases. In addition, the n-type drive transistor 23 causes the current Ib to flow as the second drain current when the gate voltage value is _VH2 . Here, the current value Imin is a current value on the horizontal axis in the current-voltage characteristic shown in FIG. 4, and a current smaller than the current value can be ignored as a light emission current.

Note that the fourth gate voltage value V _L1 corresponding to the minimum current value Imin that flows through the organic EL element in the current-voltage characteristics of the p-type drive transistor 22 is set smaller than the third gate voltage value V _H0 . It is preferable.

  As a result, the range of the gate voltage for flowing the first drain current by the p-type drive transistor 22 and the range of the gate voltage for flowing the second drain current by the n-type drive transistor 23 do not overlap and are completely separated. The As a result, the organic EL element 25 is caused to emit light by the drain current supplied from only one of the drive transistors at all data voltages without adding a switching circuit between the high voltage power line and the low voltage power line. It becomes possible.

The potential difference between the second gate voltage value V _H1 and the third gate voltage value V _H0 of the n-type drive transistor 23 is the fourth gate voltage value V _L1 of the p-type drive transistor 22 and the first gate voltage. It is preferable that the potential difference with the value V _L2 is smaller. Furthermore, it is preferable that the potential difference between the second gate voltage value V _H1 and the third gate voltage value V _H0 of the n-type drive transistor 23 is as small as possible.

The drain current supplied to the organic EL element 25 starts to flow when the gate voltage corresponding to the fourth gate voltage value _VL1 is applied to the gate electrode of the p-type drive transistor 22, and the first drain current starts to flow. as the current increases, the gate voltage is reduced to the first gate voltage V _L2. When the first drain current value reaches a predetermined current value Ia, a voltage corresponding to the second gate voltage value V _H1 is applied to the gate electrode of the n-type drive transistor 23, so that the second drain current flows. start. That is, the voltage range in which neither the p-type drive transistor 22 nor the n-type drive transistor 23 passes current is a voltage range corresponding to the range between the fourth gate voltage value V _L1 and the second gate voltage value V _H1. It is. By reducing this range, that is, by making the slope of the current-voltage characteristic of the n-type drive transistor 23 in that range steep, the second gate voltage value V _H1 is as low as possible (V _H1 ′ → V _H1 ) can be set, the voltage for flowing the second drain current flowing through the second drive transistor can be reduced, and the power consumption can be reduced.

The potential difference between the fourth gate voltage value V _L1 and the first gate voltage value V _L2 of the p-type drive transistor 22 is the second gate voltage value V _H1 of the n-type drive transistor 23 and the third gate voltage. It is preferable that the potential difference is larger than the value V _H0 . The potential difference between the fourth gate voltage value V _L1 and the first gate voltage value V _L2 of the p-type drive transistor 22 is used as the second gate voltage value V _H1 and the third gate voltage value V _H0 of the n-type drive transistor 23. The number of displayable gradations in the low gradation region can be increased. The reason is described below.

The data voltage applied to each gate electrode of the p-type drive transistor 22 and the n-type drive transistor 23 is applied with a predetermined minimum resolution. For example, if 0.01V is the minimum resolution, a data voltage can be input in units of 0.01V. Therefore, for example, the potential difference between the second gate voltage value V _H1 and the third gate voltage value V _H0 of the n-type drive transistor 23 is set to 0.5 V, and the fourth gate voltage value of the p-type drive transistor 22 is set. Assume that the potential difference between V _L1 and the first gate voltage value V _L2 is set to 1V. In this case, 50 gradations can be assigned in the drain current range of Ia or less between the potential difference between the second gate voltage value V _H1 and the third gate voltage value V _H0 of the n-type drive transistor 23. On the other hand, between the potential difference between the fourth gate voltage value V _L1 and the first gate voltage value V _L2 of the p-type drive transistor 22, 100 gradations can be assigned in the same drain current range. In the organic EL display panel 1 according to the present embodiment, the first drain current flowing through the p-type drive transistor 22 flows to the organic EL element 25 at a predetermined current value Ia or less. Therefore, the current control in the low gradation region is performed not by the number of gradations of the n-type driving transistor 23 but by the number of gradations of the p-type driving transistor 22. As a result, the number of gradations in the drain current range below the predetermined current value Ia can be set so that the outputable gradation in the low gradation region of the organic EL element 25 also increases. In particular, since the human eye has high luminance sensitivity in the low gradation range, the displayable gradation in the low gradation range increases, so that the quality of the representable color of the display device can be improved.

  Next, the voltage in the current-voltage characteristics of the p-type drive transistor 22 and the n-type drive transistor 23 described above is expressed by a gate-source voltage.

FIG. 5A is a graph showing current-voltage characteristics of the p-type drive transistor according to the exemplary embodiment of the present invention. With respect to the gate voltage value applied to the gate electrode of the p-type drive transistor 22, the gate-source voltage Vgs is a value obtained by subtracting V _DD2 that is the voltage of the source electrode from the gate voltage value. Therefore, it is possible to set the range of the data voltage for flowing the first drain current of the p-type drive transistor 22 and the range of Vgs to the same (V _L1 −V _L2 ).

As described above, from the characteristics of the drive transistor shown in FIGS. 4, 5 </ b> A, and 5 </ b> B, V _{L1 to} V _L2 are set as the data voltage range for flowing the first drain current of the p-type drive transistor 22 to the organic EL element 25. By setting V _{H1 to} V _H2 as a data voltage range for setting the second drain current of the n-type drive transistor 23 to flow through the organic EL element 25, the p-type is used in the range where the drain current is Ia or less. The first drain current of the drive transistor 22 is used as the light emission current of the organic EL element, and the second drain current of the n-type drive transistor 23 can be passed as the light emission current of the organic EL element 25 in a range where the drain current is larger than Ia. It becomes.

Next, regarding the function of the conversion circuit 7 for causing the light emission current of the organic EL element 25 to flow continuously in accordance with the display gradation by the above-described data voltage ranges V _{L1 to} V _L2 and V _{H1 to} V _H2. explain. The conversion circuit 7 converts video data input from the outside into a converted data signal VT.

FIG. 6 is a graph showing the conversion characteristics of the conversion circuit according to the embodiment of the present invention. In the graph shown in the figure, the horizontal axis represents video data input to the conversion circuit 7 and the vertical axis represents the conversion data signal VT output from the conversion circuit 7. The video data is, for example, digital data for expressing a luminance of 256 gradations (0 to 255). The conversion characteristics of the graph are as follows: from the low gradation (0) to a predetermined intermediate gradation (for example, 127 gradation), the VT is monotonic in the range of V _{L1 to} V _{L2 as} the display gradation increases. is decreasing. Further, when the display gradation is from a predetermined intermediate gradation (for example, 128 gradation) to a high gradation, the VT monotonously increases in the range of V _{H1 to} V _{H2 as} the display gradation increases.

  The VT output from the conversion circuit 7 is input to the DA conversion circuit 41 of the data line driving circuit 4 and converted into a data voltage as an analog signal. In the present embodiment, the data line driving circuit 4 does not output the data voltage corresponding to the video data as it is, but converts the converted data signal that has been subjected to the predetermined conversion via the conversion circuit 7 into an analog signal. The resulting data voltage is supplied to the data line.

That is, when the data voltage corresponding to the converted data signal VT is in the range from V _{L2 to} V _L1 in the current-voltage characteristics of the p-type drive transistor 22, the conversion circuit 7 displays the display level of the video data corresponding to the range. The video data is converted into the converted data signal VT so that the data voltage decreases as the tone increases. On the other hand, when the data voltage corresponding to the converted data signal VT is in the range of V _H1 or more in the current-voltage characteristics of the n-type drive transistor 23, the data voltage increases as the display gradation of the video data corresponding to the range increases. Thus, the video data is converted into a converted data signal VT.

  The organic EL display panel 1 stores the above-described conversion characteristic table in, for example, a built-in memory. The conversion circuit 7 reads a conversion characteristic table from the memory and converts the video data into a conversion data signal using the table.

  According to this aspect, even when the organic EL element is driven using two drive transistors whose polarities are inverted from each other, the data voltage is in a range corresponding to the converted data signal obtained by converting the video data. Accordingly, a data voltage corresponding to the entire area from the minimum value to the maximum value of the video data can be generated.

As a result, the data voltage corresponding to the converted data signal VT is in the range from V _{L2 to} V _L1 in the current-voltage characteristic of the p-type drive transistor 22 and V _H1 in the current-voltage characteristic of the n-type drive transistor 23. Although the control for increasing / decreasing the conversion data signal corresponding to the video data is different in the above range, even when the organic EL element 25 is driven by using two drive transistors whose polarities are reversed from each other. The data voltage corresponding to the entire area from the minimum value to the maximum value of the video data can be generated.

  Hereinafter, the driving method of the organic EL display panel and the flow of various signals from when the video signal is input to the organic EL display panel of the present invention until the organic EL display panel performs a display operation will be described.

  FIG. 7A is a diagram showing the flow of various signals in the organic EL display panel according to the embodiment of the present invention. The video signal is composed of a synchronization signal and video data.

  The synchronization signal includes a vertical synchronization signal V, a horizontal synchronization signal H, and a DE (Display Enable) signal. These synchronization signals are input to the control circuit 2. The control circuit 2 receives the synchronization signal and outputs a start pulse signal to the scanning line driving circuit 3 to control the output timing of the scanning signal SCAN output from the scanning line driving circuit 3, and the data line driving circuit By outputting a synchronization signal to 4, the control for synchronizing the timing of supplying the data voltage output from the data line driving circuit 4 and the output timing of the scanning signal SCAN is performed.

  The video data is a digital luminance information signal for causing the organic EL element 25 of each light emitting pixel 6 </ b> A to emit light, and is input to the conversion circuit 7. The conversion circuit 7 converts the video data into a conversion data signal VT and outputs the converted data signal VT to the data line driving circuit 4 as in the conversion characteristics shown in FIG. The data line driving circuit 4 converts the digital conversion data signal VT into an analog data voltage by the built-in DA conversion circuit 41 and outputs it to the light emitting pixel 6A.

  FIG. 7B is a drive timing chart of the organic EL display panel according to the embodiment of the present invention. In the figure, in order from the top, the vertical synchronization signal V, the horizontal synchronization signal H, the DE signal, the video data, the converted data signal VT, the start pulse signal, the first row scanning signal SCAN_1, the second row scanning signal SCAN_2, The scanning signal SCAN_3 on the third row and the scanning signal SCAN_E on the last row are displayed in time series.

  First, the writing timing of one frame is determined by the vertical synchronizing signal V, and the writing timing to each light emitting pixel row is determined by the horizontal synchronizing signal H.

  Next, the scan signal SCAN is set to the high level sequentially in accordance with the start pulse signal, and the data voltage converted from the converted data signal VT in synchronization with the DE signal is output to the data line.

  Hereinafter, a method for driving an organic EL display panel according to an embodiment of the present invention will be described.

  FIG. 8 is a diagram showing the relationship of the operation flow of each circuit included in the organic EL display panel according to the embodiment of the present invention. FIG. 2 shows operations mainly including the control circuit 2, the scanning line driving circuit 3, the data line driving circuit 4, and the conversion circuit 7 included in the organic EL display panel 1 and the relationship between these operations.

  First, a video signal is input from the outside, and the organic EL display panel 1 inputs video data constituting the video signal to the conversion circuit 7 (S01), and inputs a synchronization signal to the control circuit 2 (S21).

  Next, the conversion circuit 7 converts the input video data into a converted data signal VT based on the conversion characteristics shown in FIG. 6 (S02). Then, the conversion circuit 7 outputs the converted conversion data signal VT to the data line driving circuit 4 (S03).

  On the other hand, the control circuit 2 to which the synchronization signal is input generates a start pulse signal from the DE signal that constitutes the input synchronization signal (S22).

  Next, the control circuit 2 outputs the DE signal to the data line driving circuit 4 and outputs the generated start pulse signal to the scanning line driving circuit 3 (S23).

  Next, the data line drive circuit 4 to which the DE signal is input converts the converted data signal VT output from the conversion circuit 7 into the data voltage Vdata by the built-in DA conversion circuit 41 (S11).

  Next, the data line driving circuit 4 sets the DA-converted data voltage in each data driver in the scanning order for each data line in order from the converted data signal VT synchronized with the DE signal (S12).

  On the other hand, the scanning line driving circuit 3 to which the start pulse signal is input generates a SCAN signal by the start pulse signal (S31).

  Next, the scanning line driving circuit 3 outputs the generated scanning signal SCAN for each scanning line (S32).

  The data line driving circuit 4 outputs the data voltage of the light emitting pixels connected to the scanning line that is at the high level by the scanning signal SCAN output from the scanning line driving circuit 3 (S13).

  Finally, the scanning line driving circuit 3 sets the scanning line that has been set to the high level in step S13 to the low level (S33).

  Hereinafter, a circuit operation of the light emitting pixel to which the scanning signal SCAN is input from the scanning line driving circuit 3 and the data voltage Vdata is input from the data line driving circuit 4 will be described.

  FIG. 9 is an operation flowchart of the light-emitting pixel circuit according to the embodiment of the present invention.

  First, the scanning line 11 is set to a high level by the scanning signal SCAN, and the selection transistor 21 of the light emitting pixel 6A is turned on (S41).

  Next, the data voltage of the light emitting pixel 6A is output from the data line driving circuit 4 to the data line 12 (S42).

  Through steps S41 and S42, a voltage corresponding to the data voltage is held in the capacitor 24 of the light emitting pixel 6A (S43).

  Next, the scanning line 11 is set to a low level by the scanning signal SCAN, and the selection transistor 21 of the light emitting pixel 6A is turned off (S44).

  Next, the p-type drive transistor 22 or the n-type drive transistor 23 is automatically turned on according to the magnitude of the applied data voltage (S45).

When the p-type drive transistor 22 is turned on in step S45, the first drain current flows from the first power supply line 14 to the organic EL element 25 through the p-type drive transistor 22 using the low voltage V _DD2 as the power supply voltage. (S47). On the other hand, when the n-type drive transistor 23 is turned on in step S45, the second drain current is supplied from the second power line 13 through the n-type drive transistor 23 using the high voltage V _DD1 as the power supply voltage. (S46).

  By step S46 or step S47, the organic EL element 25 emits light corresponding to the data voltage.

  FIG. 10 is an example of a driving timing chart for explaining in detail the driving operation of the organic EL display panel according to the embodiment of the present invention. The drive timing chart shown in the same figure is an excerpt of 4 horizontal periods of 4 pixels of the same data line in the drive timing chart shown in FIG. 7B, and specific data voltage values are set. The video data corresponding to the first to fourth lines are D1 to D4, respectively. The converted data signal VT and the data voltage corresponding to D1 to D4 are V1 to V4, respectively. In addition, drain currents flowing through the organic EL element 25 by the data voltages V1 to V4 are Id1 to Id4, respectively.

  Each of the video data D1 to D4 is converted into a converted data signal VT and a data voltage according to the conversion characteristics shown in FIG.

  FIG. 11 is a graph showing an example of the conversion characteristics of the conversion circuit according to the embodiment of the present invention. As shown in the figure, the video data D1 to D4 have progressively higher gradations from low gradation D1 to high gradation D4. D1 and D2 are converted into V1 and V2, respectively, using a conversion characteristic region in which the data voltage becomes lower as the video data becomes higher gradation. On the other hand, D3 and D4 are converted into V3 and V4, respectively, using a conversion characteristic region in which the data voltage increases as the video data becomes higher gradation.

  FIG. 12 is a diagram illustrating a circuit state of the light emitting pixels in the adjacent row according to the embodiment of the present invention. This figure shows a path through which a drain current flows when the data voltages V1 to V4 corresponding to the video data D1 to D4 described above are written to the first row of light emitting pixels to the fourth row of light emitting pixels, respectively. Has been.

  FIG. 13 is a graph showing an example of current-voltage characteristics of two drive transistors according to the embodiment of the present invention. The figure shows the current-voltage conversion characteristics of a light-emitting pixel realized by two drive transistors. In addition, the magnitudes of the drain currents Id1 to Id4 when the above-described data voltages V1 to V4 are written to the first to fourth rows of light emitting pixels are shown.

The graphs shown in FIGS. 11 to 13 show that low gradation video data D1 and D2 are converted into V1 and V2 by the conversion circuit 7, respectively, and V1 and V2 are in the range of V _{L2 to} V _L1. As shown, the first drain currents Id1 and Id2 flow from the p-type drive transistor 22 to the organic EL element 25 using the low voltage V _DD2 as a power supply voltage. Further, the video data D3 and D4 of the high gradation, respectively, are converted by the conversion circuit 7 in V3 and V4, n-type high voltage _{V DD1} as the power supply voltage since the V3 and V4 are in the range of _V H1 _{~V H2} It shows that the second drain currents Id3 and Id4 flow from the driving transistor 23 to the organic EL element 25, respectively.

  Returning to FIG. 10 again, the drive timing chart will be described. The video data D1 to D4 are converted into converted data signals and data voltages V1 to V4, respectively, and the converted data voltages V1 to V4 are synchronized with the scanning signals SCAN1 to SCAN4 of the first to fourth rows in each row. The drain currents Id1 to Id4 are generated in each light emitting pixel after the completion of the writing operation, and the organic EL element 25 emits light. With the above operation, power consumption P1 to P4 generated in the light emitting pixels in the first to fourth rows in one frame period is expressed as follows.

P1 = Id1 × V _DD2 (Formula 1)
P2 = Id2 × V _DD2 (Formula 2)
P3 = Id3 × V _DD1 (Formula 3)
P4 = Id4 × V _DD1 (Formula 4)

According to the above formulas 1 to 4, the first power supply line 14 to which the low voltage V _DD2 is applied is used in the display operation for the low gradation video data D1 and D2. Here, in the case of a conventional circuit configuration in which a drain current corresponding to video data of all gradations is passed by one drive transistor, the second power supply line 13 to which the high voltage V _DD1 is applied is always used. become. When both are compared, low gradation image data D1 and D2 are displayed when two drive transistors are arranged and the power supply line is properly used according to the display gradation as in the organic EL display panel 1 of the present invention. The overall power consumption of the panel can be reduced in that the power consumption is reduced.

  Although the embodiment has been described above, the organic EL display panel according to the present invention is not limited to the above-described embodiment. Another embodiment realized by combining arbitrary constituent elements in the above-described embodiment, and modifications obtained by applying various modifications conceivable by those skilled in the art to the above-described embodiment without departing from the gist of the present invention. Examples and organic EL display devices incorporating the organic EL display panel according to the present invention are also included in the present invention.

  For example, in the above embodiment, the source electrode or drain electrode of the two drive transistors is connected to the anode electrode of the organic EL element 25, and the two drive transistors are arranged on the higher potential side than the organic EL element 25. However, the present invention is not limited to this configuration. Hereinafter, modifications of the circuit configuration of the light emitting pixel 6A shown in the above embodiment will be described.

  FIG. 14 is a circuit diagram of a luminescent pixel showing a modification according to the embodiment of the present invention. In the light emitting pixel 6B shown in the figure, the cathode electrode of the organic EL element 45 and the source electrode or drain electrode of the two drive transistors are connected, and the two drive transistors are on the lower potential side than the organic EL element 45. The difference from the light emitting pixel 6 </ b> A shown in the embodiment is only in that the configuration arranged in FIG.

  The organic EL display panel including the light emitting pixel 6B described in FIG. 14 has the same effect as the organic EL display panel 1 according to the above-described embodiment. Hereinafter, the same points as the configuration of the light emitting pixel 6A will not be described, and different points will be mainly described.

  The light emitting pixel 6B illustrated in FIG. 14 includes a selection transistor 21, an n-type drive transistor 42, a p-type drive transistor 43, a capacitor 24, and an organic EL element 45. A data line 12 is arranged for each light emitting pixel column, and a scanning line 11 is arranged for each light emitting pixel row.

Further, the first power supply line 34, the second power supply line 33, the reference power supply line 35, and the reference power supply line 16 are arranged for all the light emitting pixels 6B. The first power supply line 34, the second power supply line 33, the reference power supply line 15, and the reference power supply line 16 are also connected to other light emitting pixels and are connected to the power supply circuit 5. Further, the high voltage _VEE2 set to the first power supply line 34 is set higher than the low voltage _VEE1 set to the second power supply line 33, and both the second power supply line 33 and the first power supply line 34 are set. The potential is set lower than that of the reference power line.

  The selection transistor 21 is a switching transistor in which the gate electrode is connected to the scanning line 11 and one of the source electrode and the drain electrode is connected to the gate electrodes of the n-type driving transistor 42 and the p-type driving transistor 43.

  The n-type drive transistor 42 has a gate electrode connected to the first electrode of the capacitor 24, a drain electrode connected to the cathode electrode of the organic EL element 45, and a source electrode connected to the first power supply line 34. With the above connection relationship, the n-type drive transistor 42 supplies the first drain current to the organic EL element 45 in accordance with the voltage held in the capacitor 24 to cause the organic EL element 45 to emit light. The n-type drive transistor 42 is composed of an n-type thin film transistor (n-type TFT). Here, in the present modification, the first drain current is a current that flows from the reference power supply line 35 to the first power supply line 34 via the n-type drive transistor 42.

  The p-type drive transistor 43 has a gate electrode connected to the first electrode of the capacitor 24, a source electrode connected to the cathode electrode of the organic EL element 45, and a drain electrode connected to the second power supply line 33. With the above connection relationship, the p-type drive transistor 43 supplies the second drain current to the organic EL element 45 according to the voltage held in the capacitor 24 to cause the organic EL element 45 to emit light. The p-type drive transistor 43 is composed of a p-type thin film transistor (p-type TFT). Here, in the present modification, the second drain current is a current that flows from the reference power supply line 35 to the second power supply line 33 via the p-type drive transistor 43.

  The organic EL element 45 is a light emitting element having a cathode electrode connected to the drain electrode of the n-type drive transistor 42 and the source electrode of the p-type drive transistor 43, and an anode electrode connected to the reference power supply line 35. Due to the above connection relationship, the organic EL element 45 emits light when the first drain current of the n-type drive transistor 42 or the second drain current of the p-type drive transistor 43 flows.

  The capacitor 24 has a first electrode connected to the gate electrodes of the n-type drive transistor 42 and the p-type drive transistor 43, and a second electrode connected to the reference power supply line 16 to hold a voltage corresponding to the data voltage.

Here, the first drain current supplied from the n-type drive transistor 42 and the second drain current supplied from the p-type drive transistor 43 are selectively set using a predetermined current value in the current-voltage characteristics of the organic EL element 25 as a threshold value. Are set to flow through the organic EL element 45. That is, in each display gradation, one of the first drain current and the second drain current flows through the organic EL element 45, so that one of the drain currents becomes the light emission current of the organic EL element 25. In the light emitting pixel 6B, for example, in the low light emission current region, the n-type drive transistor 42 is turned on to flow the first drain current as the light emission current. In the high light emission current region, the p-type drive transistor 43 is turned on and the second drain current flows as the light emission current. Therefore, in the low light emission current region, the first drain current flows through the organic EL element 45 from the reference power supply line 35 to the second power supply line 33 where the low voltage _VEE1 is set. Therefore, in the display operation in the low light emission current region, the power consumption can be reduced as compared with the case where the drain current is supplied to the first power supply line 34.

  That is, in the light emitting pixel 6B, the number of driving transistors is increased by one as compared with a normal light emitting pixel circuit, but without adding a switching circuit between the first power supply line 34 and the second power supply line 33, By increasing the number of drive transistors by one without providing a data line and a select transistor for every two drive transistors, the first power supply line 34 and the second power supply line 33 can be changed according to the data voltage. Can be used properly. As a result, an energy-saving pixel circuit with low power consumption can be realized with a simple configuration without significantly increasing the circuit elements of the light-emitting pixels.

FIG. 15 is a graph showing current-voltage characteristics of two drive transistors included in a light emitting pixel according to a modification according to the embodiment of the present invention. Here, in this modification, the first gate voltage value is _VL2 , the second gate voltage value is _VH1 , the third gate voltage value is _VH0 , and the fourth gate voltage value. Is V _L1 .

The n-type drive transistor 42 is a data voltage in which the first gate voltage value V _L2 when the current Ia in the current-voltage characteristic of the organic EL element shown in FIG. The current-voltage characteristic is such that the gate voltage for flowing the first drain current decreases as the first drain current becomes smaller than the current Ia. In other words, it has a current-voltage characteristic in which the first drain current increases as the gate voltage increases.

On the other hand, the p-type drive transistor 43 has a third gate voltage value V _H1 corresponding to the minimum current value Imin that flows through the organic EL element 45 when the current Ia flows as the second drain current. _The voltage value is smaller than _H0 , and the current-voltage characteristic is such that the gate voltage for flowing the second drain current decreases as the second drain current becomes larger than the current Ia. In other words, it has a current-voltage characteristic in which the second drain current decreases as the gate voltage increases. Here, the current value Imin is a current value on the horizontal axis in the current-voltage characteristic shown in FIG. 15, and a current smaller than the current value can be ignored as a light emission current.

Note that the fourth gate voltage value V _L1 corresponding to the minimum current value Imin in the current-voltage characteristics of the n-type drive transistor 42 is preferably set larger than the third gate voltage value V _H0 .

  As a result, the range of the gate voltage for flowing the first drain current by the n-type drive transistor 42 and the range of the gate voltage for flowing the second drain current by the p-type drive transistor 43 do not overlap and are completely separated. The As a result, the organic EL element 45 is caused to emit light by the drain current supplied from only one of the driving transistors at all data voltages without adding a switching circuit between the high voltage power line and the low voltage power line. It becomes possible.

  For example, the organic EL display panel according to the present invention is built in a thin flat TV as shown in FIG. By incorporating the organic EL display panel according to the present invention, a thin flat TV capable of displaying images with low power consumption and high accuracy is realized.

  The present invention is particularly useful for an active organic EL flat panel display in which the luminance is varied by controlling the light emission intensity of the pixel by the pixel signal current.

DESCRIPTION OF SYMBOLS 1 Organic EL display panel 2 Control circuit 3 Scan line drive circuit 4 Data line drive circuit 5 Power supply circuit 6 Display part 6A, 6B, 100A Light emission pixel 7 Conversion circuit 11, 111 Scan line 12, 112 Data line 13, 33 2nd Power supply line 14, 34 First power supply line 15, 35, 115 Reference power supply line 16 Reference power supply line 21, 121a, 121b Select transistor 22, 43, 122 P-type drive transistor 23, 42 N-type drive transistor 24 Capacitors 25, 45, 125 Organic EL element 41 DA conversion circuit 113 High luminance power line 114 Low luminance power line 123 Switching transistor 124a, 124b Retention capacitance element 126 Diode

Claims (11)

An organic EL element;
A capacitor having a first electrode and a second electrode and holding a voltage corresponding to the data voltage;
A gate electrode is connected to the first electrode of the capacitor, a drain electrode is connected to the anode electrode of the organic EL element, and a first drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. A p-type first drive transistor that causes the organic EL element to emit light,
A gate electrode is connected to the first electrode of the capacitor, a source electrode is connected to the anode electrode of the organic EL element, and a second drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. An n-type second drive transistor that causes the organic EL element to emit light,
A data line for supplying the data voltage;
A switching transistor for causing the capacitor to hold the voltage by switching between conduction and non-conduction between the data line and the capacitor;
A first power supply line for applying a first power supply voltage to a source electrode of the first drive transistor;
A second power supply line for applying a second power supply voltage higher than the first power supply voltage to the drain electrode of the second drive transistor;
In the first driving transistor, a first gate voltage value corresponding to a predetermined current value in a current-voltage characteristic of the organic EL element is a minimum voltage in the data voltage, and the first drain current is set to the predetermined current value. A transistor having a current-voltage characteristic such that the gate voltage for flowing the first drain current increases as it becomes smaller;
In the second drive transistor, a second gate voltage value corresponding to the predetermined current value is a voltage value larger than a third gate voltage value corresponding to a minimum current value passed through the organic EL element, and An organic EL display panel, which is a transistor having a current-voltage characteristic such that a gate voltage for flowing the second drain current increases as the two-drain current becomes larger than the predetermined current value. The organic EL display according to claim 1, wherein a fourth gate voltage value corresponding to a minimum current value flowing through the organic EL element in the current-voltage characteristics of the first drive transistor is smaller than the third gate voltage value. panel. further,
A conversion circuit for converting video data into a converted data signal;
The organic EL display according to claim 2, further comprising: a DA conversion circuit that converts the converted data signal input from the conversion circuit into the data voltage, and a data line driving circuit that supplies the data voltage to the data line. panel. The conversion circuit includes:
When the data voltage corresponding to the converted data signal is in a range from the first gate voltage value to the fourth gate voltage value in the current-voltage characteristic of the first drive transistor, the data voltage corresponding to the range is selected. The converted data signal is converted so that the data voltage after conversion decreases as the display gradation of the video data increases,
When the data voltage corresponding to the converted data signal is in a range greater than or equal to the second gate voltage value in the current-voltage characteristic of the second drive transistor, the display gradation of the video data corresponding to the range is increased. The organic EL display panel according to claim 3, wherein the converted data signal is converted so as to increase the data voltage after conversion according to. further,
The organic EL display panel according to claim 3, further comprising: a scanning line driving circuit that outputs a scanning signal for controlling conduction and non-conduction of the switching transistor to the switching transistor via a scanning line. The organic EL display panel according to claim 5, wherein pixel circuits including the organic EL element, the capacitor, the first drive transistor, and the second drive transistor are arranged in a matrix. further,
A control circuit for controlling the data line driving circuit and the scanning line driving circuit;
The control circuit includes:
A timing at which the switching transistors included in each pixel circuit in one line of the matrix are turned on by the scanning line driving circuit;
The organic EL display panel according to claim 6, wherein the data line driving circuit performs control to synchronize with a timing of supplying the data voltage to each pixel circuit in the certain one line via the data line. The data line driving circuit is synchronized with a timing at which the scanning signal is output from the scanning line driving circuit to each pixel circuit in a certain line of the matrix in response to an input of a synchronizing signal from the control circuit. The organic EL display panel according to claim 7, wherein the data voltage is supplied to each pixel circuit in one line through the data line.   The organic electroluminescence display provided with the organic electroluminescence display panel of any one of Claims 1-8. An organic EL element;
A capacitor having a first electrode and a second electrode and holding a voltage corresponding to the data voltage;
A gate electrode is connected to the first electrode of the capacitor, a drain electrode is connected to the anode electrode of the organic EL element, and a first drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. A p-type first drive transistor that causes the organic EL element to emit light,
A gate electrode is connected to the first electrode of the capacitor, a source electrode is connected to the anode electrode of the organic EL element, and a second drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. An n-type second drive transistor that causes the organic EL element to emit light,
A data line for supplying the data voltage;
A switching transistor for holding the data voltage in the first electrode of the capacitor by switching between conduction and non-conduction between the data line and the capacitor;
A first power supply line for setting a first power supply voltage at a source electrode of the first drive transistor;
A second power supply line for setting a second power supply voltage higher than the first power supply voltage at the drain electrode of the second drive transistor;
A conversion circuit for converting video data into a converted data signal;
A DA conversion circuit that converts the converted data signal input from the conversion circuit into the data voltage, and the data line driving circuit that supplies the data voltage to the data line,
In the first driving transistor, a first gate voltage value corresponding to a predetermined current value in a current-voltage characteristic of the organic EL element is a minimum voltage in the data voltage, and the first drain current is set to the predetermined current value. A transistor having a current-voltage characteristic such that the gate voltage for flowing the first drain current increases as it becomes smaller;
In the second drive transistor, a second gate voltage value corresponding to the predetermined current value is a voltage value larger than a third gate voltage value corresponding to a minimum current value passed through the organic EL element, and A transistor having a current-voltage characteristic such that a gate voltage for flowing the second drain current increases as the two-drain current becomes larger than the predetermined current value;
A driving method of an organic EL display panel,
The conversion circuit includes:
The data voltage corresponding to the converted data signal is from the first gate voltage value in the current-voltage characteristics of the first drive transistor to the fourth gate voltage value corresponding to the minimum current value passed through the organic EL element. In the case of the range, a first conversion step for converting the converted data voltage so as to decrease as the display gradation of the video data corresponding to the range increases;
When the data voltage corresponding to the converted data signal is in a range greater than or equal to the second gate voltage value in the current-voltage characteristic of the second drive transistor, the display gradation of the video data corresponding to the range is increased. And a second conversion step of converting the converted data voltage so as to increase the data voltage. An organic EL element;
A capacitor having a first electrode and a second electrode and holding a voltage corresponding to the data voltage;
The gate electrode is connected to the first electrode of the capacitor, the drain electrode is connected to the cathode electrode of the organic EL element, and a first drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. An n-type first driving transistor that causes the organic EL element to emit light,
The gate electrode is connected to the first electrode of the capacitor, the source electrode is connected to the cathode electrode of the organic EL element, and a second drain current corresponding to the voltage held in the capacitor is supplied to the organic EL element. A p-type second drive transistor that causes the organic EL element to emit light,
A data line for supplying the data voltage;
A switching transistor for holding the data voltage in the first electrode of the capacitor by switching between conduction and non-conduction between the data line and the capacitor;
A first power supply line for setting a first power supply voltage at a source electrode of the first drive transistor;
A second power supply line for setting a second power supply voltage lower than the first power supply voltage at a drain electrode of the second drive transistor;
In the first drive transistor, a first gate voltage value corresponding to a predetermined current value in a current-voltage characteristic of the organic EL element is a maximum voltage in the data voltage, and the first drain current is the predetermined current value. A transistor having a current-voltage characteristic such that the gate voltage for flowing the first drain current decreases as the current decreases.
In the second driving transistor, a second gate voltage value corresponding to the predetermined current value is smaller than a third gate voltage value corresponding to a minimum current value passed through the organic EL element, and 2. An organic EL display panel, which is a transistor having a current-voltage characteristic such that the gate voltage for flowing the second drain current decreases as the 2-drain current becomes larger than the predetermined current value.

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